5
a?bb?
3
aaa

aabba
QwQ
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <vector>

using namespace std;
#define maxn 1000 + 10

int m[maxn], n;
string s;
bool flag;
int cnt;

bool judge(string str)
{
    int len = str.size();
    for(int i=0; i<len/2; i++)
    {
        if(s[i] != s[len-1-i])
            return false;
    }
    return true;
}

void dfs(int num)
{
    if(flag) return ;
    if(num == cnt)
    {
        if(!judge(s))
            {
                cout<<s<<endl;
                flag = true;
            }
          return ;
    }
    for(char i='a'; i<='z'; i++)
    {
        s[m[num]] = i;
        dfs(num + 1);
    }
    return ;
}

int main()
{
    while(~scanf("%d", &n))
    {
           flag = false;
           cnt = 0;
           cin>>s;
           memset(m, -1, sizeof(m));
           for(int i=0; i<n; i++)
           {
               if(s[i] == '?')
                m[cnt++] = i;
           }
           if(!cnt)
           {
               if(!judge(s))
                cout<<s<<endl;
               else cout<<"QwQ"<<endl;
           }
           else {
                dfs(0);
                if(!flag) cout<<"QwQ"<<endl;
           }

    }
}