#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
const long nPrime = 1000000007;
//const long nPrime = 998244353;
typedef long long ll;
int main() {
    long n;
    cin >> n;
    vector<long> viNum(n), viOrd(n+1,2);
    for(long i = 0; i < n; i++){
        cin >> viNum[i];
        viOrd[i+1] = viOrd[i]*3;
        viOrd[i] %= nPrime;
    }
    long nAns = 0;
    long iThis = 1;
    for(long i = 0; i < n-1; i++){
        iThis *= viNum[i];
        iThis %= nPrime;
        nAns += iThis * viOrd[n-i-2];
        nAns += nPrime;
    }
    nAns += iThis * viNum[n-1];
    nAns %= nPrime;
    cout << nAns << endl;
    
    return 0;
}