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

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define MOD 998244353
using ll = long long int;

int mod_div(int x, int y) {
  //return (long long)x * mod_inv(y) % MOD;
  int z = MOD, u = 1, v = 0;
  while (z) {
    int t = y / z;
    y -= t * z; swap(y, z);
    u -= t * v; swap(u, v);
  }
  u %= MOD;
  if (u < 0) u += MOD;
  return (long long)x * u % MOD;
}

int mod_factorial (int x) {
  int ret = 1;
  while (x > 1) {
    ret = ((ll)ret * (ll)x) % MOD;
    x--;
  }
  return ret;
}

int main() {
  int N, K;
  cin >> N >> K;
  string S;
  cin >> S;
  int n = 0, nn = 0;
  rep(i, N) {
    if (S[i] == 'N') {
      if (i == 0)
	n++;
      else if (S[i-1] != 'C')
	n++;
    }
    if (S[i] == 'N')
      nn++;
  }
  int ans = 0;
  // nCr = nPr / r! = n! / (n-r)!*r!
  int nu = mod_factorial(n);
  rep(i, nn - K) {
    if (i+1 > n) break;
    int de = ((ll)mod_factorial(n-(i+1))* (ll)mod_factorial(i+1)) % MOD;
    int cnr = mod_div(nu, de) % MOD;
    ans = ((ll)ans + (ll)cnr) % MOD;
  }
  cout << ans << endl;
  return 0;
}