#include <bits/stdc++.h>
using namespace std;
char tt[10] = {"AGTC"};
int main() {
  int a, n, k, b;
  char str[1005];
  while (scanf("%d", &n) != EOF) {
    getchar();
    scanf("%s", str);
    int vis[1005] = {0};
    for (int i = 0; i < n; i++) {
      vis[str[i]]++;
    }
    int j = 0;
    int flag = 1;
    if (vis['A'] <= n / 4 && vis['T'] <= n / 4 && vis['C'] <= n / 4 &&
        vis['G'] <= n / 4) {
      for (int i = 0; i < n; i++) {
        if (str[i] == '?' && vis[tt[j]] < n / 4) {
          str[i] = tt[j];
          vis[tt[j]]++;
        } else if (str[i] == '?') {
          if (j == 3) break;
          j++;
          i--;
        }
      }
    } else {
      flag = 0;
    }
    for (int i = 0; i < n; i++) {
      if (str[i] == '?') {
        flag = 0;
        break;
      }
    }
    if (flag) {
      cout << str << endl;
    } else {
      printf("===\n");
    }
  }
  return 0;
}
