#include <bits/stdc++.h>
#include <atcoder/modint>
using mint = atcoder::modint998244353;
using ll = long long;
using namespace std;

vector<mint> f0, f1;
void init(int n) {
    f0.resize(n + 1);
    f0[0] = 1;
    for (int i = 1; i <= n; i++) {
        f0[i] = f0[i - 1] * i;
    }
    f1.resize(n + 1);
    f1[n] = f0[n].inv();
    for (int i = n; i > 0; i--) {
        f1[i - 1] = f1[i] * i;
    }
}
mint comb(int n, int k) {
    if (n < k || k < 0) return 0;
    return f0[n] * f1[k] * f1[n - k];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, k;
    cin >> n >> k;

    string s;
    cin >> s;

    init(n);

    int c = 0, d = 0;
    for (int i = 0; i < n; i++) {
        c += (i == 0 || s[i - 1] != 'C') && s[i] == 'N';
        d += s[i] == 'N';
    }

    mint x = 0;
    for (int i = 1; i <= d - k; i++) {
        x += comb(c, i);
    }
    cout << x.val() << endl;

    return 0;
}