#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define all(v) (v).begin(), (v).end()
#define pb push_back
#define int ll

void dbg_out() { cerr << endl; }
template<typename H, typename... T>
void dbg_out(H h, T... t) { cerr << ' ' << h; dbg_out(t...); }
#define dbg(...) { cerr << #__VA_ARGS__ << ':'; dbg_out(__VA_ARGS__); }

const int N = 21;
const int NA = 100;
const int NAC = 300;

// bitset<NAC> memo[N][N][NA];
// bool memo[N][N][NA][NAC];
// char pai[N][N][NA]

void solve() {
    int n, k; cin >> n >> k;
    string s; cin >> s;

    if (n == 1) {
        if (k != 0) {
            cout << "-1";
            return;
        }
        cout << (s == "?" ? "A" : s) << "\n";
        return;
    }

    // no inverso vai ser CAN
    // using Tbool = vector(n, vector (n, vector (n, vector<bool>())));
    // using Tarray = vector(n, vector (n, vector (n, vector<array<int, 4>>())));
    auto calc = [&] (string ref = "NAC", string cur) {
        dbg (ref);
        int n = cur.size();
        vector memo (n + 1, vector(N, vector (NA, vector<bool> (NAC))));
        vector pai (n + 1, vector(N, vector (NA, vector<array<int, 5>> (NAC))));

        memo[0][0][0][0] = 1;
        for (int i = 1; i <= n; i++) {
            char u = cur[i - 1];
            if (u == ref[0] || u == '?') {
                for (int qn = 0; qn < N; qn++)
                    for (int qna = 0; qna < NA; qna++)
                        for (int qnac = 0; qnac < NAC; qnac++) if (qn + 1 < N && memo[i - 1][qn][qna][qnac]) {
                            memo[i][qn + 1][qna][qnac] = 1;
                            pai[i][qn + 1][qna][qnac] = {i - 1, qn, qna, qnac, ref[0]};
                        }
            } 
            if (u == ref[1] || u == '?') {
                for (int qn = 0; qn < N; qn++)
                    for (int qna = 0; qna < NA; qna++)
                        for (int qnac = 0; qnac < NAC; qnac++) if (qna + qn < NA && memo[i - 1][qn][qna][qnac]) {
                            memo[i][qn][qna + qn][qnac] = 1;
                            pai[i][qn][qna + qn][qnac] = {i - 1, qn, qna, qnac, ref[1]};
                        }
            } 
            if (u == ref[2] || u == '?') {
                for (int qn = 0; qn < N; qn++)
                    for (int qna = 0; qna < NA; qna++)
                        for (int qnac = 0; qnac < NAC; qnac++) if (qnac + qna < NAC && memo[i - 1][qn][qna][qnac]) {
                            memo[i][qn][qna][qnac + qna] = 1;
                            pai[i][qn][qna][qnac + qna] = {i - 1, qn, qna, qnac, ref[2]};
                        }
            }
            if (u == '?' || (u != ref[0] && u != ref[1] && u != ref[2])) {
                for (int qn = 0; qn < N; qn++)
                    for (int qna = 0; qna < NA; qna++)
                        for (int qnac = 0; qnac < NAC; qnac++) if (memo[i - 1][qn][qna][qnac]) {
                            memo[i][qn][qna][qnac] = 1;
                            pai[i][qn][qna][qnac] = {i - 1, qn, qna, qnac, 'B'};
                        }
            }
        }

        return pair{memo, pai};
    };

    auto recover = [&] (auto &memo, auto &pai, string &r, int i, int qn, int qna, int qnac) {
        string res;
        while (i > 0) {
            auto [ii, qqn, qqna, qqnac, c] = pai[i][qn][qna][qnac];
            // dbg (i, qn, qna, qnac, c);
            res += char (c);
            i = ii;
            qn = qqn;
            qna = qqna;
            qnac = qqnac;
        }
        reverse(all(res));
        return res;
    };
    
    string s_esq = s.substr (0, n / 2);
    string s_dir = s.substr (n / 2, n - n / 2);

    reverse(all(s_dir));

    dbg (s_esq, s_dir);

    auto [memo_esq, pai_esq] = calc ("NAC", s_esq);
    auto [memo_dir, pai_dir] = calc ("CAN", s_dir);

    for (int qn = 0; qn < N; qn++)
        for (int qna = 0; qna < NA; qna++)
            for (int qnac = 0; qnac < NAC; qnac++) if (memo_esq[s_esq.size()][qn][qna][qnac]) {
                for (int qqn = 0; qqn < N; qqn++)
                    for (int qqna = 0; qqna < NA; qqna++) {
                        int tot = qnac;
                        tot += qn * qqna;
                        tot += qna * qqn;
                        int qqnac = k - tot;
                        if (0 <= qqnac && qqnac < NAC && memo_dir[s_dir.size()][qqn][qqna][qqnac]) {
                            auto ans_esq = recover (memo_esq, pai_esq, s_esq, s_esq.size(), qn, qna, qnac);
                            auto ans_dir = recover (memo_dir, pai_dir, s_dir, s_dir.size(), qqn, qqna, qqnac);
                            reverse(all(ans_dir));

                            string ans = ans_esq + ans_dir;

                            for (int i = 0; i < n; i++) if (s[i] != '?') ans[i] = s[i];
                            cout << ans << "\n";
                            exit (0);
                        }
                    }
            }

    cout << "-1\n";

    // auto [memo_esq, pai] = calc ("NAC", s);

    // for (int qn = 0; qn < N; qn++)
    //     for (int qna = 0; qna < NA; qna++) if (memo[n][qn][qna][k]) {
    //         dbg (n, qn, qna, k);
    //         dbg (recover (memo, pai, s, n, qn, qna, k));
    //         exit (0);
    //     }
}

signed main() {
	ios::sync_with_stdio(false); cin.tie(0);
	solve();
}