#include<bits/stdc++.h>
#define rep(i,j,k) for (int i=(j);i<=(k);++i)
#define dep(i,j,k) for (int i=(j);i>=(k);--i)
#define MAXN 500
#define MOD 998244353
using namespace std;
typedef long long LL;

LL dp[MAXN+5][MAXN+5],sum[MAXN+5][MAXN+5];
int a[MAXN+5];
LL nCr[MAXN+5][MAXN+5];

void init() {
    nCr[0][0]=1;
    rep(i,1,MAXN) nCr[i][0]=1;
    rep(i,1,MAXN) {
        rep(j,1,i) {
            nCr[i][j]=(nCr[i-1][j-1]+nCr[i-1][j])%MOD;
        }
    }
}

void solve() {
    init();
    int n;
    cin>>n;
    rep(i,1,n) cin>>a[i];
    int tot=0;
    dep(i,n,1) {
        if (!a[i]) {
            rep(j,1,tot+1) dp[i][j]=dp[i+1][j];
            rep(j,1,tot+1) sum[i][j]=sum[i+1][j];
            continue;
        }
        tot+=a[i];
        dp[i][tot+1]=1;
        rep(j,a[i]+1,tot) {
            dp[i][j]=(dp[i+1][j-a[i]]+nCr[j-1][a[i]-1]*sum[i+1][j-a[i]+1]%MOD)%MOD;
        }
        dep(j,tot+1,1) {
            sum[i][j]=(sum[i][j+1]+dp[i][j])%MOD;
        }
    }
    cout<<sum[1][1]<<"\n";
    return;
}

int main() {
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t;
    // cin>>t;
    t=1;
    while (t--) solve();
    return 0;
}