N=int(input())
A=tuple(map(int,input().split()))
MOD=998244353
inv=[None]+[1]+[None]*(3*10**5+100)

for a in range(2, len(inv)):
  inv[a] = -(MOD // a)*inv[MOD % a]
  inv[a] %= MOD

fac=[1, 1]+[None]*(3*10**5)
for i in range(2, len(fac)):
  fac[i] = (fac[i-1]*i)%MOD

facInv=[1, 1]+[None]*(3*10**5)
for i in range(2, len(facInv)):
  facInv[i] = (facInv[i-1]*inv[i])%MOD

ans = 1

for i in range(len(A)):
  ans += fac[A[i]-1+i+1]*facInv[A[i]-1]*facInv[i+1]
  ans %= MOD

print(ans)