#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2")
#include <bits/stdc++.h>
#define INF 1000000001LL
#define LNF 1000000000000000001LL
#define MOD 998244353LL
#define MAX 100001
#define long long long
#define all(x) x.begin(),x.end()
using namespace std;

vector<long> fac(300001);
long power(long a, long b)
{
    if(b == 1)
        return a;
    long c = power(a,b/2);
    if(b&1)
        return (((c*c)%MOD)*a)%MOD;
    else
        return ((c*c)%MOD);
}

long modinv(long k)
{
    return power(k,MOD-2);
}

long nCr(long n, long r)
{
    if(r < 0)
        return 0;
    if(r > n)
        return 0;
    long up = fac[n];
    long down = fac[r]*(fac[n-r])%MOD;

    return (up*modinv(down))%MOD;
}

long trans(int x, int y)
{
    int xx = x+y;
    int yy = y;
    return nCr(xx,yy);
}
int main()
{
	ios_base::sync_with_stdio(0); 
    cin.tie(0);

    int n;    
    cin >> n;
    vector<long> arr(n);
    
    fac[0] = 1;
    for(int i = 0; i<n; i++)
        cin >> arr[i];

    for(int i = 1; i<300001; i++)
        fac[i] = fac[i-1]*i%MOD;
    arr.push_back(0);
    long res = 0;
    for(int i = 0; i<n; i++)
    {
        for(int j = arr[i+1]; j<arr[i]; j++)
            res+=trans(i,j);
        res+=trans(i,arr[i]-1);
    }

    cout << res%MOD << endl;

    

    return 0;
}