#include <bits/stdc++.h>
using namespace std;
int n;
char c[100005];
int main() {
  cin >> n;
  cin >> c + 1;
  int A, G, C, T;
  A = G = C = T = 0;
  for (int i = 1; i <= n; i++) {
    if (c[i] == 'A') A++;
    if (c[i] == 'G') G++;
    if (c[i] == 'C') C++;
    if (c[i] == 'T') T++;
  }
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  if (A > n / 4 || G > n / 4 || C > n / 4 || T > n / 4) {
    cout << "===";
    return 0;
  }
  int NA, NG, NC, NT;
  NA = n / 4 - A, NG = n / 4 - G;
  NC = n / 4 - C, NT = n / 4 - T;
  for (int i = 1; i <= n; i++) {
    if (c[i] != '?') {
      cout << c[i];
      continue;
    }
    if (NA) {
      cout << "A";
      NA--;
      continue;
    }
    if (NC) {
      cout << "C";
      NC--;
      continue;
    }
    if (NG) {
      cout << "G";
      NG--;
      continue;
    }
    if (NT) {
      cout << "T";
      NT--;
      continue;
    }
  }
  return 0;
}
