#include <bits/stdc++.h>
#include <atcoder/convolution>
using namespace std;
const long long MOD = 998244353;
long long modpow(long long a, long long b){
	long long ans = 1;
	while (b > 0){
		if (b % 2 == 1){
			ans *= a;
			ans %= MOD;
		}
		a *= a;
		a %= MOD;
		b /= 2;
	}
	return ans;
}
long long modinv(long long a){
	return modpow(a, MOD - 2);
}
vector<long long> mf = {1};
vector<long long> mfi = {1};
long long modfact(int n){
	if (mf.size() > n){
		return mf[n];
	} else {
		for (int i = mf.size(); i <= n; i++){
			long long next = mf.back() * i % MOD;
			mf.push_back(next);
			mfi.push_back(modinv(next));
		}
		return mf[n];
	}
}
long long modfactinv(int n){
	if (mfi.size() > n){
		return mfi[n];
	} else {
		return modinv(modfact(n));
	}
}
int main(){
  int N;
  long long M;
  cin >> N >> M;
  vector<int> K(N);
  for (int i = 0; i < N; i++){
    cin >> K[i];
  }
  queue<vector<long long>> Q;
  vector<long long> C(5001, 0);
  for (int i = 0; i < N; i++){
    C[K[i]]++;
  }
  Q.push(C);
  for (int i = 1; i < N; i++){
    vector<long long> f = {(M + i) % MOD, MOD - 1};
    Q.push(f);
  }
  while (Q.size() >= 2){
    vector<long long> f = Q.front();
    Q.pop();
    vector<long long> g = Q.front();
    Q.pop();
    Q.push(atcoder::convolution(f, g));
  }
  vector<long long> a = Q.front();
  int cnt = a.size();
  long long ans = 0;
  for (int i = 0; i < cnt; i++){
    for (int j = 0; j <= M; j++){
      ans += a[i] * modpow(j, i);
      ans %= MOD;
    }
  }
  ans *= modfactinv(N - 1);
  ans %= MOD;
  cout << ans << endl;
}