MOD = 998244353

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

pow2 = [1]
for _ in range(n):
    pow2.append(pow2[-1] * 2 % MOD)

ans = 0
for i in range(n):
    ans += pow2[n - 1 - i] * A[i] % MOD
    ans -= pow2[i] * A[i] % MOD
    ans %= MOD
    
print(ans)