How to check if a string is a palindrome:  

         a b c d e d c b a  
         ^               ^
         |               | 
       1st letter     last letter  



 Palindrome test:

    test1:   1st letter == last   letter
    test2:   2nd letter == last-1 letter
    test3:   3rd letter == last-2 letter 
    and so on !!!


    If all tests are passed ---> the string is a palindrome


  

  To check whether:      x pass all the tests test1, test2, ... , testk do:

     (1) Assume that x passes  // Initial assumption

     (2) For each test testi:
             check if x passes the test testi
             if x fails, then x did not pass all tests 


  boolean passAllTest = true;  // Initial assumption

  for ( each test "test i" )
  {
     if ( x fails to pass test "test i" )
     {
        passAllTest = false;   // x did not pass all tests
     }
  }

  // Here: the variable passAllTest = true if all tests passed
  

       Given a string x  (e.g.: "level" or "abc")

   x must pass these palindrome tests:

         1st character = last   character  
         2nd character = last-1 character  
         .... 
 

  boolean isPalindrome = true;  // Assume it is a palindrone

  for ( i = 0; i < x.length(); i++ )
  {
     if ( character i in string x   !=   character last - i in string x )
     {
        isPalindrome = false;  // Fail: x is not a palindrome
     }
  }

  // Unsolved problems:  how to find character i in string x
                         how to find character last - i in string x

   // Why last = length() - 1:            "abcd"   length() = 4
   //                         index pos:   0123       
   //                                         ^ last =3 = 4 - 1 = length() - 1  

   public static void main(String[] args) 
   {
      Scanner input = new Scanner(System.in);
      
      String x = input.next();

      int i, last;       // Index of the characters that we are comparing

      last = x.length() - 1;

      boolean isPalindrome = true;    // Initial assumption

      for ( i = 0; i < x.length(); i++ )
      {
          if ( x.charAt( i )  !=  x.charAt( last-i ) )
          {
              isPalindrome = false;  // x is not a palindrome
          }
      }
      System.out.println(isPalindrome);
   } 

   // Why last = length() - 1:            "abcd"   length() = 4
   //                         index pos:   0123       
   //                                         ^ last =3 = 4 - 1 = length() - 1  

   public static void main(String[] args) 
   {
      Scanner input = new Scanner(System.in);
      
      String x = input.next();

      int i, last;       // Index of the characters that we are comparing

      last = x.length() - 1;

      boolean isPalindrome = true;    // Initial assumption

      for ( i = 0; i < x.length()/2; i++ )
      {
          if ( x.charAt( i )  !=  x.charAt( last-i ) )
          {
              isPalindrome = false;  // x is not a palindrome
          }
      }
      System.out.println(isPalindrome);
   } 

   // Why last = length() - 1:            "abcd"   length() = 4
   //                         index pos:   0123       
   //                                         ^ last =3 = 4 - 1 = length() - 1  

   public static void main(String[] args) 
   {
      Scanner input = new Scanner(System.in);
      
      String x = input.next();

      int i, last;       // Index of the characters that we are comparing

      last = x.length() - 1;

      boolean isPalindrome = true;    // Initial assumption

      for ( i = 0; i < x.length()/2; i++ )
      {
          if ( x.charAt( i )  !=  x.charAt( last-i ) )
          {
              isPalindrome = false;  // x is not a palindrome
              break;                 // Skip the remaining tests..
          }
      }
      System.out.println(isPalindrome);
   } 

  How to check if a number is prime:

      n = 41

      Divide the number by:   2   3   4  ....   40 (= n-1)





 Prime number tests:

    n%2     != 0
    n%3     != 0
    ...
    n%(n-1) != 0


 If n passes all these tests, then n is a prime number

 
  

  To check whether:      n pass the tests (test 1, test 2, ... , test k)

     (1) Assume that n passes  // Initial assumption

     (2) For each test test i:
             check if n passes the test test i
             if n fails, then n did not pass all tests 



  boolean passAllTest = true;  // Initial assumption

  for ( each test "test i" )
  {
     if ( n fails to pass test "test i" )
     {
        passAllTest = false;   // n did not pass all tests

     }
  }

  // When the for-loop ends, "passAllTest = true" if n passes all the tests

       Given integer n

   n must pass these tests:

         n%2 != 0
         n%3 != 0
         ....
         n%(n-1) != 0


  boolean isPrime = true;  // Initial assumption

  for ( i = 2; i < n; i++ )
  {
     if ( n%i == 0 )
     {
        isPrime = false;   // n is NOT a prime number

     }
  }

 

   public static void main(String[] args) 
   {
      Scanner input = new Scanner(System.in);
      
      int n = input.nextInt();
      boolean isPrime = true;
      int i;

      for ( i = 2; i < n; i++ )
      {
          if ( n%i == 0 )
          {
             isPrime = false;
            
          }
          
      }
      System.out.println(isPrime);
   }

   public static void main(String[] args) 
   {
      Scanner input = new Scanner(System.in);
      
      int n = input.nextInt();
      boolean isPrime = true;
      int i;

      for ( i = 2; i < n; i++ )
      {
          if ( n%i == 0 )
          {
             isPrime = false;
             break;
          }
          
      }
      System.out.println(isPrime);
   }