#include <bits/stdc++.h>
using namespace std;
char w[260];
int main() {
  int ca = 0, cg = 0, cc = 0, ct = 0, num = 0, sizee = 0, qst = 0, lol = 0;
  bool flag = false;
  scanf("%d", &lol);
  scanf("%s", w);
  sizee = strlen(w);
  num = sizee / 4;
  for (int i = 0; i < sizee; i++) {
    if (w[i] == 'A')
      ca++;
    else if (w[i] == 'G')
      cg++;
    else if (w[i] == 'C')
      cc++;
    else if (w[i] == 'T')
      ct++;
    else
      qst++;
  }
  for (int i = 0; i < sizee; i++) {
    if (w[i] == '?') {
      if (ca < num) {
        w[i] = 'A';
        ca++;
      } else if (cg < num) {
        w[i] = 'G';
        cg++;
      } else if (cc < num) {
        w[i] = 'C';
        cc++;
      } else if (ct < num) {
        w[i] = 'T';
        ct++;
      } else
        continue;
    }
  }
  ca = 0;
  cg = 0;
  cc = 0;
  ct = 0;
  for (int i = 0; i < sizee; i++) {
    if (w[i] == '?') {
      printf("===\n");
      return 0;
    } else if (w[i] == 'A')
      ca++;
    else if (w[i] == 'C')
      cc++;
    else if (w[i] == 'G')
      cg++;
    else if (w[i] == 'T')
      ct++;
  }
  if (ca == num && cg == num && cc == num && ct == num)
    printf("%s\n", w);
  else
    printf("===\n");
  return 0;
}
