#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n % 4) {
    cout << "===";
    return 0;
  }
  int A = 0, C = 0, G = 0, T = 0;
  char c[256];
  for (int i = n; i > 0; i--) {
    cin >> c[i];
    switch (c[i]) {
      case ('A'): {
        A++;
        if (A > (n / 4)) {
          cout << "===";
          return 0;
        }
        break;
      }
      case ('C'): {
        C++;
        if (C > (n / 4)) {
          cout << "===";
          return 0;
        }
        break;
      }
      case ('G'): {
        G++;
        if (G > (n / 4)) {
          cout << "===";
          return 0;
        }
        break;
      }
      case ('T'): {
        T++;
        if (T > (n / 4)) {
          cout << "===";
          return 0;
        }
        break;
      }
    }
  }
  int x = n / 4;
  while (n) {
    if (c[n] == '?') {
      if (x > A) {
        cout << "A";
        A++;
        n--;
        continue;
      }
      if (x > C) {
        cout << "C";
        C++;
        n--;
        continue;
      }
      if (x > G) {
        cout << "G";
        G++;
        n--;
        continue;
      }
      if (x > T) {
        cout << "T";
        T++;
        n--;
        continue;
      }
    } else {
      cout << c[n];
      n--;
    }
  }
}
