#include<cstdio>

using namespace std;

int len,bo;
char s[1010];

int main()
{
    while(scanf("%d",&len)!=EOF)
    {
        scanf("%s",s);
        bo=0;
        int last=len+5,cnt=0,nlast=0;
        for(int i=0;i<len;i++)
        {
            if(s[i]=='?')s[i]='a',cnt++,nlast=last,last=i;
        }
        if(last==len-last-1&&cnt!=1)last=nlast;
        for(int i=0;i<len;i++)if(s[i]!=s[len-i-1]){bo=1;break;}
        if((last==len+5||(last==len-last-1&&cnt==1))&&!bo)
        {
            puts("QwQ");
            continue;
        }
        if(!bo)s[last]='b';
        puts(s);
    }
}