#include <bits/stdc++.h>
using namespace std;
string x;
char X;
int main() {
  long long ar[256] = {0}, A = 0, T = 0, C = 0, G = 0, W = 0, n, i = 0, mx = 0;
  cin >> n >> x;
  if (n % 4 == 0) {
    for (i = 0; i < n; i++) {
      if (x[i] == 'A') {
        A++;
      }
      if (x[i] == 'T') {
        T++;
      }
      if (x[i] == 'C') {
        C++;
      }
      if (x[i] == 'G') {
        G++;
      }
      if (x[i] == '?') {
        W++;
      }
    }
    for (i = 0; i < n; i++) {
      if (x[i] == '?') {
        mx = max(max(A, C), max(G, T));
        if (A < mx) {
          x[i] = 'A';
          A++;
        } else if (T < mx) {
          x[i] = 'T';
          T++;
        } else if (C < mx) {
          x[i] = 'C';
          C++;
        } else {
          x[i] = 'G';
          G++;
        }
      }
    }
    mx = max(max(A, C), max(G, T));
    if (A != mx || T != mx || C != mx || G != mx)
      cout << "===";
    else
      cout << x;
  } else {
    cout << "===";
  }
}
