#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, i, a = 0, g = 0, c = 0, t = 0, q = 0, max;
  cin >> n;
  char str[n];
  scanf("%s", &str);
  if (n % 4 != 0) {
    cout << "===";
  } else {
    int flag = 0;
    for (i = 0; i < n; i++) {
      if (str[i] == 'A')
        a++;
      else if (str[i] == 'G')
        g++;
      else if (str[i] == 'C')
        c++;
      else if (str[i] == 'T')
        t++;
      else
        q++;
    }
    if (a >= g)
      max = a;
    else
      max = g;
    if (c > max) max = c;
    if (t > max) max = t;
    if (max == 0) {
      for (i = 0; i < n; i++) {
        if (i % 4 == 0)
          str[i] = 'A';
        else if (i % 4 == 1)
          str[i] = 'G';
        else if (i % 4 == 2)
          str[i] = 'C';
        else
          str[i] = 'T';
      }
    } else if ((q - ((max - a) + (max - g) + (max - c) + (max - t))) % 4 == 0 &&
               (q - ((max - a) + (max - g) + (max - c) + (max - t))) >= 0) {
      while (a != max) {
        for (i = 0; i < n; i++) {
          if (str[i] == '?') {
            str[i] = 'A';
            break;
          }
        }
        a++;
        q--;
      }
      while (g != max) {
        for (i = 0; i < n; i++) {
          if (str[i] == '?') {
            str[i] = 'G';
            break;
          }
        }
        g++;
        q--;
      }
      while (c != max) {
        for (i = 0; i < n; i++) {
          if (str[i] == '?') {
            str[i] = 'C';
            break;
          }
        }
        c++;
        q--;
      }
      while (t != max) {
        for (i = 0; i < n; i++) {
          if (str[i] == '?') {
            str[i] = 'T';
            break;
          }
        }
        t++;
        q--;
      }
      if (q != 0) {
        int k = 0;
        for (i = 0; i < n; i++) {
          if (str[i] == '?') {
            if (k % 4 == 0)
              str[i] = 'A';
            else if (k % 4 == 1)
              str[i] = 'G';
            else if (k % 4 == 2)
              str[i] = 'C';
            else
              str[i] = 'T';
            k++;
          }
        }
      }
    } else
      flag = 1;
    if (flag == 0)
      printf("%s", str);
    else
      cout << "===";
  }
}
