// #include C {
#include<cstring>
#include<cassert>
#include<cstdio>
#include<cctype>
#include<cmath>
// }

// #include C++ {
#include<functional>
#include<algorithm>
#include<iostream>
#include<numeric>
#include<vector>
#include<string>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<list>
#include<map>
#include<set>
// }
using namespace std;
// #typedef {
typedef long long int64;
typedef unsigned long long uint64;
typedef pair <int, int> PII;
typedef pair <int64, int64> PLL;
typedef pair <double, double> PDD;
// }

// #parameter{
#define LEN 2
#ifdef DEBUG_MODE

#define TYPE decltype
#define RF(filename) {freopen((filename), "r", stdin);}
#define WF(filename) {freopen((filename), "w", stdout);}
#define DEBUG printf

#else

#define TYPE __typeof
#define RF(filename) {;}
#define WF(filename) {;}
#define DEBUG(...)

#endif

// #define {
#define SZ(a) ((int)(a).size())
#define X first
#define Y second
#define MP make_pair
#define L(x) ((x)<<1)
#define R(x) ((x)<<1 | 1)
#define max3(x, y, z) (max(max((x), (y)), (z)))
#define min3(x, y, z) (min(min((x), (y)), (z)))
#define BIT(x, i) (((x) >> (i)) & 1)
#define ALL(it) (it).begin(), (it).end()
#define FOR(it, c) for( TYPE((c).begin()) it = (c).begin(); it != (c).end(); it++)
/////////////////////////////////////////////////////////////
const double PI = acos(-1.0);
const double EPS = 1e-6;

#define MAX_N 1005
#define MAX_M 5005
#define MAXX 0x3f
#define UPPER 2147483647LL
#define INF ((1 << 30) - 1)
#define BINF ((1LL << 62) - 1LL)
#define NONE -1
#define NIL 0
// }

/////////////////////////////////////////////////////////////
char s[MAX_N];
bitset <MAX_N> mark;
int n;
bool found;
void DFS(int depth){
    if (found) return;
    if (depth == n){
        bool palindrome = true;
        for (int i = 0, j = n - 1; i < j; i++, j--){
            if (s[i] != s[j]){
                palindrome = false;
                break;
            }
        }
        if (palindrome)
            return;
        puts(s);
        found = true;
        return;
    }
    if (mark[depth]){
        for (char ch = 'a'; ch <= 'z' && !found; ch++){
            s[depth] = ch;
            DFS(depth + 1);
        }
    }
    else
        DFS(depth + 1);
}
/////////////////////////////////////////////////////////////
int main(){
    RF("input.txt");
    //WF("output.txt");

    while (~scanf("%d", &n)){
        scanf("%s", s);
        mark.reset();
        for (int i = 0; i < n; i++) if(s[i] == '?')
            mark[i] = true;
        found = false;
        DFS(0);
        if (!found)
            puts("QwQ");
    }
    return 0;
}