#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  string s;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  vector<long long> v(5, 0);
  for (long long i = 0; i < n; i++) {
    if (s[i] == 'A') {
      v[0]++;
    }
    if (s[i] == 'C') {
      v[1]++;
    }
    if (s[i] == 'G') {
      v[2]++;
    }
    if (s[i] == 'T') {
      v[3]++;
    }
    if (s[i] == '?') {
      v[4]++;
    }
  }
  long long max1 = max(v[0], max(v[1], v[2]));
  long long maxov = max(max1, v[3]);
  long long reqd = 4 * maxov - v[0] - v[1] - v[2] - v[3];
  bool check = false;
  if (v[4] >= reqd && (v[4] - reqd) % 4 == 0) {
    check = true;
  }
  if (check == false) {
    cout << "===";
  } else {
    long long reqda = maxov - v[0] + ((v[4] - reqd) / 4);
    long long reqdc = maxov - v[1] + ((v[4] - reqd) / 4);
    long long reqdg = maxov - v[2] + ((v[4] - reqd) / 4);
    long long reqdt = maxov - v[3] + ((v[4] - reqd) / 4);
    for (long long i = 0; i < n; i++) {
      if (s[i] != '?') {
        cout << s[i];
      } else {
        if (reqda > 0) {
          cout << "A";
          reqda--;
          continue;
        }
        if (reqdc > 0) {
          cout << "C";
          reqdc--;
          continue;
        }
        if (reqdg > 0) {
          cout << "G";
          reqdg--;
          continue;
        }
        if (reqdt > 0) {
          cout << "T";
          reqdt--;
        }
      }
    }
  }
  return 0;
}
