import java.util.HashMap;

public class Solution {
    public int longestPalindrome(String s) {
        int length = 0;
        Map<Character, Boolean> map = new HashMap<>();

        for (Character ch: s.toCharArray()) {
            if (map.get(ch) != null) {
                map.remove(ch);
                length += 2;
            } else {
                map.put(ch, Boolean.TRUE); 
            }
        }

        return map.isEmpty() ? length : ++length;
    }
}