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

const int MOD = 998244353;

int binpow(int a, int p) {
    if (p == 1) return a;
    if (p % 2 == 0) {
        int x = binpow(a, p / 2);
        return (x * x) % MOD;
    }
    return (binpow(a, p - 1) * a) % MOD;
}

int cnk(int n, int k) {
    int num = 1;
    int den = 1;
    for (int i = k + 1; i <= n; i++) {
        num *= i;
        num %= MOD;
    }
    for (int i = 1; i <= n - k; i++) {
        den *= i;
        den %= MOD;
    }
    return (num * binpow(den, MOD - 2)) % MOD;
}

signed main() {
    int n;
    cin >> n;
    int arr[n];
    for(int i = 0; i < n; i++) cin >> arr[i];
    int dp[n + 1] = {};
    dp[n] = 1;
    for (int i = n - 1; i >= 0; i--) {
        if (arr[i] >= 0) {
        for (int j = i + arr[i] + 1; j < n + 1; j++) {
            dp[i] += (cnk(j - i - 1, arr[i]) * dp[j]);
            dp[i] %= MOD;
        }
        }
    }
    int ans = 0;
    for (int i = 0; i < n; i++) ans += dp[i];
    ans %= MOD;
    cout << ans;
}
