N = int(input())
L = list(map(int,input().split()))
L = L[::-1]
S = 0
mod = 998244353
S = 1
SUM = L[0]
ans = 0
for i in range(1,len(L)):
    ans += L[i]*S - SUM
    SUM += (SUM + L[i])
    SUM %= mod
    S += (S+1)
    S %= mod
print(ans%mod)