#include <bits/stdc++.h>
using namespace std;
char v[10000];
int a[10];
int main() {
  int n;
  memset(a, 0, sizeof(a));
  scanf("%d", &n);
  int sum = n / 4;
  scanf("%s", v);
  for (int i = 0; i < n; i++) {
    if (v[i] == 'A') a[0]++;
    if (v[i] == 'G') a[1]++;
    if (v[i] == 'C') a[2]++;
    if (v[i] == 'T') a[3]++;
  }
  for (int i = 0; i < n; i++) {
    if (v[i] == '?') {
      for (int j = 0; j < 4; j++) {
        if (a[j] < sum) {
          if (j == 0) v[i] = 'A';
          if (j == 1) v[i] = 'G';
          if (j == 2) v[i] = 'C';
          if (j == 3) v[i] = 'T';
          a[j]++;
          break;
        }
      }
    }
  }
  int flag = 0;
  for (int i = 0; i < 4; i++) {
    if (a[i] == sum)
      continue;
    else
      flag = 1;
  }
  for (int i = 0; i < n; i++) {
    if (v[i] == '?') flag = 1;
  }
  if (flag == 1) {
    printf("===\n");
  } else {
    for (int i = 0; i < n; i++) {
      printf("%c", v[i]);
    }
    printf("\n");
  }
  return 0;
}
