#include <stdio.h>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
char str[1100]={0};
int a[1100]={0};
int judge()
{
for(int i=0,j=strlen(str)-1;i<j;i++,j--)
if(str[i]!=str[j])
return 0;
return 1;
}
int main()
{
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
int n;
while(scanf("%d",&n)!=EOF)
{
memset(str,0,sizeof(str));
memset(a,0,sizeof(a));
int c=0,flag=0,flag1=0;
scanf("%s",str);
for(int i=0;i<n;i++)
if(str[i]=='?')
{
flag=1;
str[i]='a';
a[c++]=i;
}
if(flag)
{
if(judge()&&c)
str[a[c-1]]='b';
c--;
while(judge()&&c)
{
str[a[c]]='a';
str[a[c-1]]='b';
c--;
}
if(judge()&&n>=2)
printf("QwQ\n");
else
printf("%s\n",str);
}
else
printf("QwQ\n");
}
return 0;
}
