#include <bits/stdc++.h>
using namespace std;
int n;
string s;
map<char, int> vis;
int main() {
  scanf("%d", &n);
  cin >> s;
  if (n % 4 != 0) {
    printf("===\n");
    return 0;
  }
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != '?') {
      vis[s[i]]++;
      if (vis[s[i]] > n / 4) {
        printf("===\n");
        return 0;
      }
    }
  }
  int num = n / 4;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != '?')
      cout << s[i];
    else {
      if (vis['A'] < num) {
        cout << 'A';
        vis['A']++;
        continue;
      }
      if (vis['T'] < num) {
        cout << 'T';
        vis['T']++;
        continue;
      }
      if (vis['G'] < num) {
        cout << 'G';
        vis['G']++;
        continue;
      }
      if (vis['C'] < num) {
        cout << 'C';
        vis['C']++;
        continue;
      }
    }
  }
  cout << endl;
}
