#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, n, a = 0, g = 0, c = 0, t = 0, y = 0, m, aa, bb, cc, dd, ee = 0;
  scanf("%d", &n);
  char ch[300];
  cin >> ch;
  for (int i = 0; i < n; i++) {
    if (ch[i] == 'A')
      a++;
    else if (ch[i] == 'G')
      g++;
    else if (ch[i] == 'C')
      c++;
    else if (ch[i] == 'T')
      t++;
    else if (ch[i] == '?')
      y++;
  }
  m = max(max(max(a, g), c), t);
  aa = m - a;
  bb = m - g;
  cc = m - c;
  dd = m - t;
  if (y - ((m - a) + (m - g) + (m - c) + (m - t)) >= 0 &&
      (y - ((m - a) + (m - g) + (m - c) + (m - t))) % 4 == 0) {
    for (int i = 0; i < n; i++) {
      if (ch[i] == '?') {
        if (aa > 0) {
          printf("A");
          aa--;
          y--;
        } else if (bb > 0) {
          printf("G");
          bb--;
          y--;
        } else if (cc > 0) {
          printf("C");
          cc--;
          y--;
        } else if (dd > 0) {
          printf("T");
          dd--;
          y--;
        } else {
          if (ee == 0) {
            printf("A");
          } else if (ee == 1) {
            printf("G");
          } else if (ee == 2) {
            printf("C");
          } else if (ee == 3) {
            printf("T");
          }
          ee++;
          ee %= 4;
        }
      } else {
        printf("%c", ch[i]);
      }
    }
  } else {
    printf("===\n");
  }
}
