n=int(input())
A=list(map(int,input().split()))
p=998244353
def kaimod(n,p):
  l=[1]
  a=1
  for i in range(1,n+1):
    a=(a*i)%p
    l+=[a]
  b=pow(a,p-2,p)
  ll=[1]*(n+1)
  ll[n]=b
  for i in range(n-1,1,-1):
    b=(b*(i+1))%p
    ll[i]=b
  return([l,ll])
q=kaimod(a[0]+n,p)
kai=q[0]
kair=q[1]
ans=2
for i in range(1,n-1):
	if A[i]>A[i+1]:
		ans=(ans+((kai[i+A[i]-1]*kair[i])%p)*kair[A[i]-1])%p
print(ans)