#include <bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
using mint=modint998244353;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)

int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    rep(i, 0, N){
    	cin >> A[i];
    }
    
    int L = A[0];
    vector<mint> fact(L + 1, 1), fact_inv(L + 1, 1);
    rep(i, 1, L + 1) fact[i] = fact[i - 1] * i;
    fact_inv[L] = fact[L].inv();
    for(int i = L; i > 0; i--){
    	fact_inv[i - 1] = fact_inv[i] * i;
    }
    
    mint ans = 0;
    vector<mint> dp(N);
    auto f = [&](auto self, int l, int r) -> void {
    	if(l + 1 == r){
    		dp[l] += fact[A[l]];
    		ans += dp[l] * fact_inv[A[l]];
    		return;
    	}
    	int m = (l + r) / 2;
    	self(self, l, m);
    	vector<mint> X(A[l] - A[m - 1] + 1), Y(A[l] - A[r - 1] + 1);
    	rep(i, l, m) X[A[l] - A[i]] += dp[i];
    	rep(i, 0, Y.size()) Y[i] += fact_inv[i];
    	X = convolution(X, Y);
    	rep(i, m, r) dp[i] += X[A[l] - A[i]];
    	self(self, m, r);
    };
    f(f, 0, N);
    cout << ans.val() << "\n";
}