#include <bits/stdc++.h>

#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

class mint{
	static const int MOD=998244353;
	int x;
public:
	mint():x(0){}
	mint(long long y){ x=y%MOD; if(x<0) x+=MOD; }

	mint& operator+=(const mint& m){ x+=m.x; if(x>=MOD) x-=MOD; return *this; }
	mint& operator-=(const mint& m){ x-=m.x; if(x<   0) x+=MOD; return *this; }
	mint& operator*=(const mint& m){ x=1LL*x*m.x%MOD; return *this; }
	mint& operator/=(const mint& m){ return *this*=inverse(m); }
	mint operator+(const mint& m)const{ return mint(*this)+=m; }
	mint operator-(const mint& m)const{ return mint(*this)-=m; }
	mint operator*(const mint& m)const{ return mint(*this)*=m; }
	mint operator/(const mint& m)const{ return mint(*this)/=m; }
	mint operator-()const{ return -x; }

	friend mint inverse(const mint& m){
		int a=m.x,b=MOD,u=1,v=0;
		while(b>0){ int t=a/b; a-=t*b; swap(a,b); u-=t*v; swap(u,v); }
		return u;
	}

	friend istream& operator>>(istream& is,mint& m){ long long t; is>>t; m=t; return is; }
	friend ostream& operator<<(ostream& os,const mint& m){ return os<<m.x; }
	int to_int()const{ return x; }
};

mint operator+(long long x,const mint& m){ return mint(x)+m; }
mint operator-(long long x,const mint& m){ return mint(x)-m; }
mint operator*(long long x,const mint& m){ return mint(x)*m; }
mint operator/(long long x,const mint& m){ return mint(x)/m; }

int n,a[2500];

int d;
bool vis[2501][2501];
mint memo[2501][2501];

mint dfs(int i,int l,int r){
	if(vis[l][r]) return memo[l][r];
	vis[l][r]=true;

	mint& res=memo[l][r];
	if(i==-1) return res=1;

	res=0;
	if(l-a[i]<=d) res+=dfs(i-1,a[i],r);
	if(r-a[i]<=d) res+=dfs(i-1,l,a[i]);
	return res;
}

int main(){
	scanf("%d",&n);
	rep(i,n) scanf("%d",&a[i]);

	vector<mint> res(2500);
	for(d=1;d<2500;d++){
		memset(vis,0,sizeof vis);
		res[d]=dfs(n-2,a[n-1],a[n-1]);
	}

	mint ans=0;
	for(d=1;d<2500;d++) ans+=d*(res[d]-res[d-1]);
	cout<<ans<<'\n';

	return 0;
}