#include <bits/stdc++.h>   using namespace std;   const int MAXN = 1e3 + 10;   const int MOD = 998244353;   const int INF = 10;   int fact[MAXN], invfact[MAXN];   int add(int a, int b) {     int sum = a + b;     return (sum >= MOD ? sum -= MOD : (sum < 0 ? sum += MOD : sum));   }   int mul(int a, int b) { return 1LL * a * b % MOD; }   int pwr(int a, int b) {     return (!b ? 1                : (b & 1 ? 1LL * a * pwr(1LL * a * a % MOD, b >> 1) % MOD                         : pwr(1LL * a * a % MOD, b >> 1) % MOD));   }   int inv(int x) { return pwr(x, MOD - 2); }   void first() {     fact[0] = 1;     for (int i = 1; i < MAXN; i++) fact[i] = mul(fact[i - 1], i);     for (int i = 0; i < MAXN; i++) invfact[i] = inv(fact[i]);   }   int C(int n, int k) { return mul(mul(fact[n], invfact[k]), invfact[n - k]); }   int P(int n, int k) { return mul(fact[n], invfact[n - k]); }   int n, a[MAXN], dp[MAXN];   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     first();     cin >> n;     for (int i = 0; i < n; i++) {       cin >> a[i];     }     dp[n] = 1;     for (int i = n - 1; i >= 0; i--) {       if (a[i] <= 0 || a[i] + i - 1 > n - 1) {         continue;       }       for (int j = n - 1; j >= a[i] + i; j--) {         dp[i] = add(dp[i], mul(dp[j + 1], C(j - i, a[i])));       }     }     int ans = 0;     for (int i = 0; i < n; i++) {       ans = add(ans, dp[i]);     }     cout << ans;     return 0;   }   