#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<ll>;
const ll INF = LLONG_MAX / 4;
#define rep(i, a, b) for(ll i = a; i < (b); i++)
#define all(a) begin(a), end(a)
#define sz(a) ssize(a)
bool chmin(auto& a, auto b) { if(a <= b) return 0; a = b; return 1; }
bool chmax(auto& a, auto b) { if(a >= b) return 0; a = b; return 1; }

using A = array<ll, 3>;
map<A, string> half(string S) {
    map<A, string> a;
    a[{0, 0, 0}];
    for(char c : S) {
        map<A, string> b;
        auto add = [&](char c) {
            for(auto [key, val] : a) {
                auto [n, na, nac] = key;
                if(c == 'N') n += 1;
                if(c == 'A') na += n;
                if(c == 'C') nac += na;
                val.push_back(c);
                b[{n, na, nac}] = val;
            }
        };
        if(c == '?') for(char cc : "NACB"s) add(cc);
        else add(c);
        swap(a, b);
    }
    return a;
}
int main() {
    cin.tie(0)->sync_with_stdio(0);

    ll n, k;
    cin >> n >> k;
    string S;
    cin >> S;

    string S1 = S.substr(0, n / 2), S2(rbegin(S), rend(S) - n / 2);
    for(char& c : S2) if(c == 'N' || c == 'C') c ^= 'N' ^ 'C';

    auto H1 = half(S1), H2 = half(S2);
    auto at = [&](array<ll, 3> a) {
        ll i = a[0];
        i *= 10 * 10 + 1;
        i += a[1];
        i *= 6 * 7 * 7 + 1;
        i += a[2];
        return i;
    };
    vector<bool> exists(at({21, 0, 0}));
    for(auto& [key, val] : H2) {
        exists[at(key)] = 1;
    }
    for(auto& [key, S1] : H1) {
        const auto [n, na, nac] = key;
        rep(c, 0, 21) rep(ca, 0, 101) {
            const ll can = k - nac - n * ca - na * c;
            if(can > 6 * 7 * 7) continue;
            if(can < 0) break;
            if(!exists[at({c, ca, can})]) continue;
            auto S2 = H2[{c, ca, can}];
            ranges::reverse(S2);
            for(char& c : S2) if(c == 'N' || c == 'C') c ^= 'N' ^ 'C';
            cout << S1 << S2 << endl;
            return 0;
        }
    }
    puts("-1");
}