#include <bits/stdc++.h>
using namespace std;
struct comp {
  bool operator()(int a, int b) { return a > b; }
};
int main() {
  int n, countA = 0, countC = 0, countG = 0, countT = 0;
  char data[500];
  scanf("%d\n%s", &n, &data);
  if (n % 4 != 0) {
    printf("===\n");
  } else {
    for (int i = 0; i < n; i++) {
      if (data[i] == 'A')
        countA++;
      else if (data[i] == 'C')
        countC++;
      else if (data[i] == 'G')
        countG++;
      else if (data[i] == 'T')
        countT++;
    }
    int tmp = n / 4;
    if (countA > tmp || countC > tmp || countG > tmp || countT > tmp) {
      printf("===\n");
    } else {
      for (int i = 0; i < n; i++) {
        if (data[i] == '?') {
          if (countA < tmp)
            countA++, printf("A");
          else if (countC < tmp)
            countC++, printf("C");
          else if (countG < tmp)
            countG++, printf("G");
          else if (countT < tmp)
            countT++, printf("T");
        } else {
          printf("%c", data[i]);
        }
      }
      printf("\n");
    }
  }
  return 0;
}
