#include <bits/stdc++.h>

std::bitset<2501> dp[42][42][409];

int main() {
    int n, k;
    std::cin >> n >> k;

    std::string s;
    std::cin >> s;
    s = ' ' + s;

    auto check = [&](char c, char t) {
        return c == t || c == '?';
    };

    dp[0][0][0].set(0);
    for (int i = 1; i <= n; ++i) {
        for (int x = 0; x <= i; ++x) {
            for (int y = 0; y <= (i / 2) * (i - i / 2); ++y) {
                // null
                if (s[i] != 'N' && s[i] != 'A' && s[i] != 'C') {
                    dp[i][x][y] |= dp[i - 1][x][y];
                }
                // N
                if (check(s[i], 'N') && x >= 1) {
                    dp[i][x][y] |= dp[i - 1][x - 1][y];
                }
                // A
                if (check(s[i], 'A') && y >= x) {
                    dp[i][x][y] |= dp[i - 1][x][y - x];
                }
                // C
                if (check(s[i], 'C')) {
                    dp[i][x][y] |= dp[i - 1][x][y] << y;
                }
            }
        }
    }

    auto output = [&](auto self, int n, int x, int y, int k) -> void {
        if (n == 0) {
            return;
        }
        if (s[n] != 'N' && s[n] != 'A' && s[n] != 'C' && dp[n - 1][x][y][k]) {
            self(self, n - 1, x, y, k);
            std::cout << (s[n] == '?' ? 'F' : s[n]);
        } else if (check(s[n], 'N') && x >= 1 && dp[n - 1][x - 1][y][k]) {
            self(self, n - 1, x - 1, y, k);
            std::cout << "N";
        } else if (check(s[n], 'A') && y >= x && dp[n - 1][x][y - x][k]) {
            self(self, n - 1, x, y - x, k);
            std::cout << "A";
        } else if (check(s[n], 'C') && k >= y && dp[n - 1][x][y][k - y]) {
            self(self, n - 1, x, y, k - y);
            std::cout << "C";
        } else {
            assert(false);
        }
    };
    
    for (int x = 0; x <= n; ++x) {
        for (int y = 0; y <= (n / 2) * (n - n / 2); ++y) {
            if (dp[n][x][y].test(k)) {
                output(output, n, x, y, k);
                return 0;
            }
        }
    }

    std::cout << "-1\n";
}