import java.util.*;

public class Palindrome {

    public static void main (String[] argv)
    {
	// Test 1.
        String str = "redder";
        System.out.println ( str + " " + checkPalindrome(str) );

	// Test 2.
        str = "river";
        System.out.println ( str + " " + checkPalindrome(str) );

	// Test 3.
        str = "neveroddoreven";
        System.out.println ( str + " " + checkPalindrome(str) );
    }
    

    static String checkPalindrome (String str)
    {
	// Extract the letters.
	char[] letters = str.toCharArray ();

	// Create an empty stack.
	Stack<Character> stack = new Stack<Character>();

	// The letters must "balance" up to the middle.
	int mid = letters.length / 2;

	// Push the first half.
	for (int i=0; i<mid; i++) {
	    stack.push (letters[i]);
	}

	// Odd or even? We have to adjust the mid-point accordingly.
	if (letters.length % 2 > 0) {
	    // Odd number => swallow middle letter.
	    mid = mid+1;
	}

	// Now check the second half.
	for (int i=mid; i<letters.length; i++) {
	    char ch = stack.pop ();
	    if (ch != letters[i]) {
		// Mismatch => not a palindrome.
		return "is not a palindrome";
	    }
	}

	return "is a palindrome";
    }

}