#include <bits/stdc++.h>
using namespace std;
char st[260];
int main() {
  int N, num = 0, na = 0, ng = 0, nc = 0, nt;
  scanf("%d %s", &N, st);
  for (int i = 0; i < N; i++) {
    if (st[i] == '?')
      num++;
    else if (st[i] == 'A')
      na++;
    else if (st[i] == 'T')
      nt++;
    else if (st[i] == 'C')
      nc++;
    else if (st[i] == 'G')
      ng++;
  }
  int nl = N / 4;
  if (N % 4 || na > nl || nt > nl || nc > nl || ng > nl)
    printf("===\n");
  else {
    for (int i = 0; i < N; i++)
      if (st[i] == '?') {
        if (na < nl)
          st[i] = 'A', na++;
        else if (nt < nl)
          st[i] = 'T', nt++;
        else if (nc < nl)
          st[i] = 'C', nc++;
        else if (ng < nl)
          st[i] = 'G', ng++;
      }
    cout << st;
  }
  return 0;
}
