//
//  main.cpp
//  dima
//
//  Created by Irina Korneeva on 23/05/2019.
//  Copyright © 2019 Irina Korneeva. All rights reserved.
//

#include <iostream>
#include <vector>
using namespace std;
int main(int argc, const char * argv[]) {
    int n;
    cin >> n;
    long long ans = 0;
    long long mod = 1000000007;
    vector<long long> data(101, 0);
    long long res = 1;
    data[0] = res;
    for(int i = 1; i <= 100; i++) {
        res = (res * 2) % mod;
        data[i] = res;
    }
    long long a = 1;
    long long b = 2;
    int x, y;

    cin >> x;
    a = (a * data[x]) % mod;
    for(int i = 2; i < n + 1; i++) {
        cin >> y;
        b = (b * data[y]) % mod;
        long long r = b;
        b = (a + b) % mod;
        a = r;
    }
    cout << b;
}