#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 9;
char s[maxn];
int num[4];
char sol(int a) {
  if (a == 0) return 'A';
  if (a == 1) return 'C';
  if (a == 2) return 'G';
  if (a == 3) return 'T';
}
int main() {
  int a, b, c, d, e, f, g, h;
  while (scanf("%d", &a) == 1) {
    scanf("%s", s);
    if (a % 4) {
      printf("===\n");
      continue;
    }
    memset(num, 0, sizeof(num));
    for (d = 0; d < a; d++) {
      if (s[d] == 'A') {
        num[0]++;
      } else if (s[d] == 'C') {
        num[1]++;
      } else if (s[d] == 'G') {
        num[2]++;
      } else if (s[d] == 'T') {
        num[3]++;
      }
    }
    g = 1;
    for (d = 0; d < 4; d++) {
      if (num[d] > a / 4) {
        g = 0;
        break;
      }
      num[d] = a / 4 - num[d];
    }
    if (!g) {
      printf("===\n");
      continue;
    }
    for (d = 0; d < a; d++) {
      if (s[d] == '?') {
        for (e = 0; e < 4; e++) {
          if (num[e]) {
            printf("%c", sol(e));
            num[e]--;
            break;
          }
        }
      } else
        printf("%c", s[d]);
    }
    printf("\n");
  }
  return 0;
}
