#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, aa = 0, g = 0, c = 0, t = 0;
  int sssss = 0;
  int used[300] = {0};
  string a;
  cin >> n >> a;
  for (int i = 0; i < n; i++) {
    if (a[i] == '?')
      used[i] = 1, sssss++;
    else if (a[i] == 'A')
      aa++;
    else if (a[i] == 'G')
      g++;
    else if (a[i] == 'C')
      c++;
    else if (a[i] == 'T')
      t++;
  };
  int max = aa;
  if (max < c) max = c;
  if (max < g) max = g;
  if (max < t) max = t;
  max +=
      (sssss - (abs(max - aa) + abs(max - c) + abs(max - g) + abs(max - t))) /
      4;
  for (int i = 0; i < n; i++) {
    if (used[i]) {
      if (aa < max)
        a[i] = 'A', aa++;
      else if (c < max)
        a[i] = 'C', c++;
      else if (g < max)
        a[i] = 'G', g++;
      else if (t < max)
        a[i] = 'T', t++;
      else {
        cout << "===";
        return 0;
      }
    };
  };
  if (aa < max || c < max || g < max || t < max) {
    cout << "===";
    return 0;
  }
  cout << a;
  return 0;
};
