n = int(input()); mod = 998244353; ans = 0
for i, v in enumerate(map(int, input().split())):
    if i < n-1: ans = (ans+v*(pow(2, n-i-1, mod)-1))%mod
    if i > 0: ans = (ans-v*(pow(2, i, mod)-1))%mod
print(ans)