#include<bits/stdc++.h>
#define IL inline
#define reg register
#define N 2020
#define mod 998244353
IL int read()
{
    reg int x=0; reg char ch=getchar();
    while(ch<'0'||ch>'9')ch=getchar();
    while(ch>='0'&&ch<='9')x=x*10+ch-'0',ch=getchar();
    return x;
}

IL int Add(reg int x,reg int y){return x+y<mod?x+y:x+y-mod;}
IL void Pls(reg int &x,reg int y){x=Add(x,y);}
IL int Mul(reg int x,reg int y){reg long long r=1ll*x*y; return r<mod?r:r%mod;}

int fac[N],ifac[N],inv[N];

IL void init(reg int n)
{
    fac[0]=ifac[0]=inv[1]=1;
    for(reg int i=2;i<=n;++i)inv[i]=Mul(mod-mod/i,inv[mod%i]);
    for(reg int i=1;i<=n;++i)fac[i]=Mul(fac[i-1],i),ifac[i]=Mul(ifac[i-1],inv[i]);
}

IL int C(reg int n,reg int m){return Mul(fac[n],Mul(ifac[m],ifac[n-m]));}

int n,a[N],f[N],ans;

IL int min(reg int x,reg int y){return x<y?x:y;}

int mn[N][N];

main()
{
    n=read(),init(2e3);
    for(reg int i=0;i<=n;++i)a[i]=read();
    for(reg int k=1,i;k<=n+1;++k)for(i=n;~i;--i)
    {
        mn[k][i]=a[i];
        if(i+k<=n)mn[k][i]=min(mn[k][i],mn[k][i+k]);
    }
    for(reg int p=0,q,k,w,i;p<=n;++p) // f0 = 0
    {
        for(q=p;q<=n-(!!p);++q)
        {
            k=q-p+1;
            if(q<=n/2) 
            {
                w=1;
                for(i=p;i<=q;++i)
                {
                    reg int x=min(n/2,mn[k][i]);
                    if(x>=i)w=Mul(w,(x-i)/k+1);
                    else w=0;
                }
                Pls(ans,w);
            }else
            {
                w=1;
                for(i=p;i<=q&&w;++i)if(mn[k][i]<i){w=0; break;}
                Pls(ans,w);
            }
        }
        if(a[p]<p)break;
    }
    printf("%d\n",ans);
}