#include <bits/stdc++.h>
using namespace std;
int maxx(int*);
int arr[4];
int main() {
  int n, i, k, count1 = 0, max, maxi, a, g, c, t, counta, countb, countc,
               countd;
  counta = countb = countc = countd = 0;
  string str;
  cin >> n >> str;
  if (n % 4 != 0) {
    cout << "===" << '\n';
    return 0;
  }
  for (i = 0; i < n; i++) {
    if (str[i] == 'A')
      arr[0]++;
    else if (str[i] == 'G')
      arr[1]++;
    else if (str[i] == 'C')
      arr[2]++;
    else if (str[i] == 'T')
      arr[3]++;
    else if (str[i] == '?')
      count1++;
  }
  maxi = n / 4;
  if (arr[0] > maxi || arr[1] > maxi || arr[2] > maxi || arr[3] > maxi) {
    cout << "===" << '\n';
    return 0;
  }
  k = 0;
  for (i = 0; i < 4; i++) {
    arr[i] = maxi - arr[i];
  }
  a = arr[0], g = arr[1], c = arr[2], t = arr[3];
  for (i = 0; i < n; i++) {
    if (str[i] != '?')
      continue;
    else {
      while (arr[k] == 0 && k < 4) k++;
      if (k == 0) {
        str[i] = 'A';
        counta++;
      } else if (k == 1) {
        str[i] = 'G';
        countb++;
      } else if (k == 2) {
        str[i] = 'C';
        countc++;
      } else if (k == 3) {
        str[i] = 'T';
        countd++;
      }
      arr[k]--;
    }
  }
  cout << str << '\n';
  return 0;
}
