// MagicDark
#include <bits/stdc++.h>
#define debug cerr << "\033[32m[" << __LINE__ << "]\033[0m "
#define SZ(x) ((int) x.size() - 1)
#define all(x) x.begin(), x.end()
#define ms(x, y) memset(x, y, sizeof x)
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define DF(i, x, y) for (int i = (x); i >= (y); i--)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template <typename T> T& chkmax(T& x, T y) {return x = max(x, y);}
template <typename T> T& chkmin(T& x, T y) {return x = min(x, y);}
template <typename T> T& read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
	return x *= f;
}
// const int N = 
// bool be;
int n, k;
string st;
bool dp[41][41][41][2510];
short pos[41][41][41][2510];
// bool ed;
signed main() {
	// debug << abs(&ed - &be) / 1024 / 1024 << endl;
	cin.tie(0) -> sync_with_stdio(0); // don't use puts
	cin >> n >> k >> st;
	st = ' ' + st;
	F(i, 0, n) dp[0][0][i][0] = true;
	F(i, 1, n) {
		if (st[i] == '?' || st[i] == 'N') { // N
			F(j, 0, i - 1)
				F(t, 0, n - (i - 1))
					F(l, 0, k)
						if (dp[i - 1][j][t][l]) {
							dp[i][j + 1][t][l] = true;
							pos[i][j + 1][t][l] = 0;
						}
		}
		if (st[i] == '?' || st[i] == 'A') { // A
			F(j, 0, i - 1)
				F(t, 0, n - (i - 1))
					F(l, 0, k - j * t) {
						if (dp[i - 1][j][t][l]) {
							dp[i][j][t][l + j * t] = true;
							pos[i][j][t][l + j * t] = 1;
						}
					}
		}
		if (st[i] == '?' || st[i] == 'C') { // C
			F(j, 0, i - 1)
				F(t, 1, n - (i - 1))
					F(l, 0, k) {
						if (dp[i - 1][j][t][l]) {
							dp[i][j][t - 1][l] = true;
							pos[i][j][t - 1][l] = 2;
						}
					}
		}
		if (st[i] != 'N' && st[i] != 'A' && st[i] != 'C') {
			F(j, 0, i - 1)
				F(t, 0, n - (i - 1))
					F(l, 0, k)
						if (dp[i - 1][j][t][l]) {
							dp[i][j][t][l] = true;
							pos[i][j][t][l] = 3;
						}
		}
	}
	// if (dp[n][])
	F(i, 0, n)
		if (dp[n][i][0][k]) {
			string ans = st;
			int a = n, b = i, c = 0, d = k;
			while (a) {
				if (pos[a][b][c][d] == 0) {
					ans[a] = 'N';
					b--;
				} else if (pos[a][b][c][d] == 1) {
					ans[a] = 'A';
					d -= b * c;
				} else if (pos[a][b][c][d] == 2) {
					ans[a] = 'C';
					c++;
				} else {
					ans[a] = 'F';
				}
				a--;
			}
			F(j, 1, n) cout << ans[j];
			return 0;
		}
	cout << - 1;
	return 0;
}
/* why?
*/