#include <string>
#include <unordered_map>
using namespace std;

class Solution {
    public:
        int longestPalindrome(string s) {
            unordered_map<char, int> count;
            int ans = 0;
            for (char c : s)
                ++count[c];
            for (auto p : count) {
                int v = p.second;
                ans += v / 2 * 2;
                if (v % 2 == 1 and ans % 2 == 0)
                    ++ans;
            }
            return ans;
        }
    };