#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N;
int A[2555];
const ll mo=998244353;

ll dp[2555];
ll num[2525];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	FOR(i,N) cin>>A[i];
	reverse(A,A+N);
	
	ll ret=0;
	for(x=1;x<=2500;x++) {
		ZERO(dp);
		if(A[0]-A[1]>x) continue;
		dp[0]=2;
		y=k=0;
		ll S=2;
		for(i=2;i<N;i++) {
			if(A[i-1]-A[i]>x) {
				ZERO(dp);
				break;
			}
			// keep
			while(y+1<i&&A[y]-A[i]>x) S+=mo-dp[y++];
			dp[i-1]=S;
			S+=dp[i-1];
			
			S%=mo;
		}
		FOR(i,N) num[x]+=dp[i];
		num[x]%=mo;
		(ret+=x*(num[x]-num[x-1]+mo))%=mo;
	}
	
	cout<<ret<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}