#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


int N, K;
char S[50];

bitset<2510> dp[50][50][810];

int main() {
  for (; ~scanf("%d%d", &N, &K); ) {
    scanf("%s", S);
    
#ifdef LOCAL
    for (int i = 0; i <= N; ++i) {
      for (int x = 0; x <= i; ++x) for (int y = 0; y <= (i/2)*(i-i/2); ++y) {
        dp[i][x][y].reset();
      }
    }
#endif
    
    dp[0][0][0].set(0);
    for (int i = 0; i <= N; ++i) {
      for (int x = 0; x <= i; ++x) for (int y = 0; y <= (i/2)*(i-i/2); ++y) {
        if (S[i] == '?' || !(S[i] == 'N' || S[i] == 'A' || S[i] == 'C')) dp[i + 1][x][y] |= dp[i][x][y];
        if (S[i] == '?' || S[i] == 'N') dp[i + 1][x + 1][y] |= dp[i][x][y];
        if (S[i] == '?' || S[i] == 'A') dp[i + 1][x][y + x] |= dp[i][x][y];
        if (S[i] == '?' || S[i] == 'C') dp[i + 1][x][y] |= dp[i][x][y] << y;
      }
    }
    int xm = -1, ym = -1;
    for (int x = 0; x <= N; ++x) for (int y = 0; y <= (N/2)*(N-N/2); ++y) if (dp[N][x][y][K]) {
      xm = x;
      ym = y;
    }
    if (~xm) {
      string ans = S;
      int x = xm, y = ym, k = K;
      for (int i = N; --i >= 0; ) {
        if (S[i] == '?' || !(S[i] == 'N' || S[i] == 'A' || S[i] == 'C')) {
          if (dp[i][x][y][k]) {
            ans[i] = (S[i] == '?') ? 'B' : S[i];
            continue;
          }
        }
        if (S[i] == '?' || S[i] == 'N') {
          if (x - 1 >= 0 && dp[i][x - 1][y][k]) {
            x -= 1;
            ans[i] = 'N';
            continue;
          }
        }
        if (S[i] == '?' || S[i] == 'A') {
          if (y - x >= 0 && dp[i][x][y - x][k]) {
            y -= x;
            ans[i] = 'A';
            continue;
          }
        }
        if (S[i] == '?' || S[i] == 'C') {
          if (k - y >= 0 && dp[i][x][y][k - y]) {
            k -= y;
            ans[i] = 'C';
            continue;
          }
        }
        assert(false);
      }
      puts(ans.c_str());
    } else {
      puts("-1");
    }
  }
  return 0;
}