#include <bits/stdc++.h>
using namespace std;
const long long MAX = 1e9;
const long long N = 1e5 + 10;
map<char, long long> cnt;
vector<long long> idx;
int32_t main() {
  long long n;
  cin >> n;
  cnt['A'] = 0;
  cnt['G'] = 0;
  cnt['C'] = 0;
  cnt['T'] = 0;
  string s;
  cin >> s;
  for (long long i = 0; i < n; i++)
    if (s[i] != '?')
      cnt[s[i]]++;
    else
      idx.push_back(i);
  while (idx.size()) {
    char m;
    long long a = INT_MAX;
    for (auto i : cnt)
      if (a > i.second) a = i.second, m = i.first;
    s[idx.back()] = m;
    cnt[m]++;
    idx.pop_back();
  }
  long long c = cnt.begin()->second;
  for (auto i : cnt)
    if (i.second != c) {
      cout << "===";
      return 0;
    }
  cout << s;
  return 0;
}
