import sys
readline=sys.stdin.readline

N=int(readline())
A=list(map(int,readline().split()))
M=2500
cnt=[0]*M
mod=998244353
for d in range(M-1,-1,-1):
    if any(A[i+1]-A[i]>d for i in range(N-1)):
        break
    dp=[0]*(N+1)
    r=N
    dp[N-1]=1
    for l in range(N-3,-1,-1):
        while A[r-1]-A[l]>d:
            r-=1
        dp[l+1]=(dp[l+2]+dp[l+2]-dp[r])%mod
    cnt[d]=dp[1]*2%mod
for i in range(M-1,0,-1):
    cnt[i]-=cnt[i-1]
    cnt[i]%=mod
ans=sum(d*cnt[d]%mod for d in range(M))%mod
print(ans)