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

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

//defmodfact
const int COMinitMAX = 998244;
mint fact[COMinitMAX+1], factinv[COMinitMAX+1];

void modfact(){
	fact[0] = 1;
	for (int i=1; i<=COMinitMAX; i++){
		fact[i] = fact[i-1] * i;
	}
	factinv[COMinitMAX] = fact[COMinitMAX].inv();
	for (int i=COMinitMAX-1; i>=0; i--){
		factinv[i] = factinv[i+1] * (i+1);
	}
}

mint cmb(int a, int b){
	if (a<b || b<0) return mint(0);
	return fact[a]*factinv[b]*factinv[a-b];
}
//--------


int main(){
	modfact();
	int n, m; cin >> n >> m;
	vector<int> b(n);
	rep(i,0,n) cin >> b[i];
	int a = m-b[0];
	
	vector<vector<mint>> dp(n, vector<mint>(a+1));
	dp[0][0] = 1;
	rep(i,1,n){
		vector<mint> x(a+1);
		vector<mint> y(a+1);
		rep(k,0,a+1){
			if (b[i-1]-k >= 0){
				x[k] = dp[i-1][k] * factinv[k] * fact[b[i-1]-k];
			}
		}
		rep(k,0,a+1){
			if (b[i-1]-b[i]+k >= 0){
				y[k] = factinv[k] * factinv[b[i-1]-b[i]+k];
			}
		}
		vector<mint> z = convolution(x, y);
		rep(j,0,a+1){
			if (b[i]-j >= 0){
				dp[i][j] = fact[j] * factinv[b[i]-j] * z[j];
			}
		}
	}
	mint ans = 0;
	rep(j,0,a+1){
		ans += dp[n-1][j] * cmb(m, b[0] + j) * cmb(b[0] + j, b[0]);
	}
	cout << ans.val() << '\n';
}