杭电新生赛（1005）

#include<iostream>
#include<cmath>
long long w = 1e9 + 7;
using namespace std;
int main()
{
    int n;
    while (cin >> n)
    {
        long long a[102];
        for (int i = 1; i <= n+1; i++)
            cin >> a[i];
        long long t = 1;
        for (int i = 1; i < n; i++)
            t = t * 2%w;
        long long s = 0;
        for (int i = 1; i <= n; i++)
        {
            s =( s + a[i] * t)%w;
        }
        s = (s + a[n+1]) % w;
        cout << s << endl;
    }
    return 0;
}