// time complexity: O(N^6)

#include <string>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

string solve(int N, int K, const string& S) {
	vector<vector<vector<vector<bool> > > > vis(N + 1, vector<vector<vector<bool> > >(N + 1, vector<vector<bool> >(N + 1, vector<bool>(K + 1, false))));
	auto check = [&](auto& self, int pos, int x, int y, int z) -> string {
		if (pos == N) {
			return (y == 0 && z == K ? "" : "-1");
		}
		if (y < 0 || z > K) {
			return "-1";
		}
		if (vis[pos][x][y][z]) {
			return "-1";
		}
		vis[pos][x][y][z] = true;
		if (S[pos] != 'N' && S[pos] != 'A' && S[pos] != 'C') {
			string res1 = self(self, pos + 1, x, y, z);
			if (res1 != "-1") {
				return (S[pos] != '?' ? S[pos] : 'B') + res1;
			}
		}
		if (S[pos] == 'N' || S[pos] == '?') {
			string res2 = self(self, pos + 1, x + 1, y, z);
			if (res2 != "-1") {
				return 'N' + res2;
			}
		}
		if (S[pos] == 'C' || S[pos] == '?') {
			string res3 = self(self, pos + 1, x, y - 1, z);
			if (res3 != "-1") {
				return 'C' + res3;
			}
		}
		if (S[pos] == 'A' || S[pos] == '?') {
			string res4 = self(self, pos + 1, x, y, z + x * y);
			if (res4 != "-1") {
				return 'A' + res4;
			}
		}
		return "-1";
	};
	string res = "-1";
	for (int y = 0; y <= N; y++) {
		string subres = check(check, 0, 0, y, 0);
		if (subres != "-1") {
			res = subres;
			break;
		}
	}
	return res;
}

int main() {
	int N, K; string S;
	cin >> N >> K >> S;
	string ans = solve(N, K, S);
	cout << ans << endl;
	return 0;
}