#include <bits/stdc++.h>
#pragma comment(linker, ”/ STACK : 38777216“
using namespace std;
const int N = 100005;
const int inf = 1000 * 1000 * 1000;
const int mod = 1000 * 1000 * 1000 + 7;
string s;
int a, b, c, d, t;
int main() {
  cin >> t >> s;
  if (t % 4 != 0) {
    cout << "===" << endl;
    return 0;
  }
  t /= 4;
  for (int i = 0; i < 4 * t; i++) {
    if (s[i] == 'A') a++;
    if (s[i] == 'C') b++;
    if (s[i] == 'G') c++;
    if (s[i] == 'T') d++;
  }
  if (a > t || b > t || c > t || d > t) {
    cout << "===" << endl;
    return 0;
  }
  a = t - a;
  b = t - b;
  c = t - c;
  d = t - d;
  for (int i = 0; i < 4 * t; i++) {
    if (s[i] != '?') continue;
    if (a > 0) {
      s[i] = 'A';
      a--;
      continue;
    }
    if (b > 0) {
      s[i] = 'C';
      b--;
      continue;
    }
    if (c > 0) {
      s[i] = 'G';
      c--;
      continue;
    }
    s[i] = 'T';
    d--;
  }
  cout << s << endl;
  return 0;
}
