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

using mint = atcoder::modint998244353;

const int MAX = 510000;
mint fac[MAX], finv[MAX], inv[MAX];

void combinit() {
    const int MOD = mint::mod();
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i;
        inv[i] = MOD - inv[MOD % i] * (MOD / i);
        finv[i] = finv[i - 1] * inv[i];
    }
}

mint comb(int n, int k){
    if (n < k) {
        return 0;
    }
    if (n < 0 || k < 0) {
        return 0;
    }
    return fac[n] * finv[k] * finv[n - k];
}

int main() {
    combinit();
    int n, k;
    string s;
    cin >> n >> k >> s;
    int ok = 0, ng = 0;
    for (int i = 0; i < n; i++) {
        if (s[i] == 'N') {
            if (i > 0 && s[i - 1] == 'C') {
                ng++;
            } else {
                ok++;
            }
        }
    }
    mint ans = mint(0);
    for (int i = 1; i <= ok; i++) {
        if (ng + (ok - i) >= k) {
            ans += comb(ok, i);
        }
    }
    cout << ans.val() << endl;
}