import java.io.*;
import java.util.*;

public class Main {
    static final int MOD = 1000000007;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        long[] qubes = new long[n + 1];
        qubes[1] = 1;
        for (int i = 2; i <= n; i++) {
            qubes[i] = qubes[i - 1] * 3 % MOD;
        }
        long base = 1;
        long ans = 0;
        for (int i = 0; i < n; i++) {
            base *= sc.nextInt();
            base %= MOD;
            ans += base * ((qubes[n - i] - qubes[n - i - 1] + MOD) % MOD) % MOD;
            ans %= MOD;
        }
        System.out.println(ans);
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public String nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}