#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <fstream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int v, w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

bool palindrome(string& s) {
    for (int i = 0, j = s.length() - 1; i < j; i++, j--)
        if (s[i] != s[j]) return false;
    return true;
}

int main() {
    int n;
    while (cin >> n) {
        string s; cin >> s;
        int _i = -1;
        for (int i = 0; i < n; i++)
            if (s[i] == '?') {
                s[i] = 'a';
                if (i * 2 + 1 != n) _i = i;
            }
        if (!palindrome(s)) {
            cout << s << endl;
            continue;
        }
        if (_i != -1) s[_i] = 'b';
        if (!palindrome(s)) {
            cout << s << endl;
            continue;
        }
        cout << "QwQ" << endl;
    }
}