using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var a = NList;
        var ans = 0L;
        var mod = 998_244_353;
        var ncr = new NCR(200001, mod);
        for (var i = 0; i < n; ++i)
        {
            ans = (ans + ncr.Calc(a[i] - 1 + i, i)) % mod;
            if (i + 1 == n || a[i] != a[i + 1]) ans = (ans + ncr.Calc(a[i] - 1 + i, i)) % mod;
            if (i + 1 < n) for (var j = a[i + 1] + 1; j < a[i]; ++j) ans = (ans + ncr.Calc(j - 1 + i, i)) % mod;
            else for (var j = 1; j < a[i]; ++j) ans = (ans + ncr.Calc(j - 1 + i, i)) % mod;
        }
        WriteLine(ans);
    }
    class NCR
    {
        int[] facts;
        int[] revFacts;
        int mod;
        public NCR(int n, int mod)
        {
            facts = new int[n + 1];
            revFacts = new int[n + 1];
            this.mod = mod;
            facts[0] = 1;
            var tmp = 1L;
            for (var i = 1; i <= n; ++i)
            {
                tmp = tmp * i % mod;
                facts[i] = (int)tmp;
            }
            tmp = Exp(facts[n], mod - 2);
            revFacts[n] = (int)tmp;
            for (var i = n; i > 1; --i)
            {
                tmp = tmp * i % mod;
                revFacts[i - 1] = (int)tmp;
            }
            revFacts[0] = 1;
        }
        public long Exp(long n, long k)
        {
            n = n % mod;
            if (k == 0) return 1;
            if (k == 1) return n;
            var half = Exp(n, k / 2);
            var result = half * half % mod;
            return ((k % 2) == 0) ? result : (result * n % mod);
        }
        public long Calc(int n, int r)
        {
            return (long)facts[n] * revFacts[r] % mod * revFacts[n - r] % mod;
        }
        /// <summary>nが大きくrが小さい場合の計算</summary>
        public long Calc2(int n, int r)
        {
            var tmp = 1L;
            for (var i = 0; i < r; ++i)
            {
                tmp = tmp * (n - i) % mod;
            }
            return tmp * revFacts[r] % mod;
        }
        public long NPR(int n, int r)
        {
            return (long)facts[n] * revFacts[r] % mod;
        }
        public long Fact(int n)
        {
            return facts[n];
        }
        public long RevFact(int n)
        {
            return revFacts[n];
        }
        public long Inverse(int n)
        {
            return (long)revFacts[n] * facts[n - 1] % mod;
        }
    }
}