import sys
input = sys.stdin.readline

mod=998244353

FACT=[1]
for i in range(1,2*10**5+1):
    FACT.append(FACT[-1]*i%mod)

FACT_INV=[pow(FACT[-1],mod-2,mod)]
for i in range(2*10**5,0,-1):
    FACT_INV.append(FACT_INV[-1]*i%mod)

FACT_INV.reverse()

def Combi(a,b):
    if 0<=b<=a:
        return FACT[a]*FACT_INV[b]%mod*FACT_INV[a-b]%mod
    else:
        return 0

N=int(input())
A=list(map(int,input().split()))

A.append(0)

ANS=0

for i in range(N):
    a=A[i]

    ANS+=Combi(i+a-1,i)

    #print(ANS)

    for j in range(a,A[i+1],-1):
        #print("!",j)
        ANS+=Combi(i+j-1,i)

    ANS%=mod

print(ANS)