#include <bits/stdc++.h>
using namespace std;
long long freq[30];
char acgt[5] = {0, 'A', 'C', 'G', 'T'};
int main() {
  long long a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q;
  string A;
  cin >> a >> A;
  if (a % 4) {
    printf("===\n");
    return 0;
  }
  memset(freq, 0, sizeof freq);
  for (b = 0; b < a; b++) {
    if (A[b] != '?') freq[A[b] - 65]++;
  }
  for (b = 1; b <= 4; b++) {
    if (freq[acgt[b] - 65] > a / 4) {
      printf("===\n");
      return 0;
    }
  }
  for (b = 0; b < a; b++) {
    if (A[b] == '?') {
      for (c = 1; c <= 4; c++) {
        if (freq[acgt[c] - 65] < a / 4) {
          printf("%c", acgt[c]);
          freq[acgt[c] - 65]++;
          break;
        }
      }
    } else
      printf("%c", A[b]);
  }
  return 0;
}
