Problem:
Score : 300 points

Problem Statement

Given are N integers A_1,\ldots,A_N.

Find the sum of A_i \times A_j over all pairs (i,j) such that 1\leq i < j \leq N, modulo (10^9+7).

Constraints

2 \leq N \leq 2\times 10^5

0 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print \sum_{i=1}^{N-1}\sum_{j=i+1}^{N} A_i A_j, modulo (10^9+7).

Sample Input 1

3
1 2 3

Sample Output 1

11

We have 1 \times 2 + 1 \times 3 + 2 \times 3 = 11.

Sample Input 2

4
141421356 17320508 22360679 244949

Sample Output 2

437235829

Solution in Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author test
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        abc177_c solver = new abc177_c();
        solver.solve(1, in, out);
        out.close();
    }

    static class abc177_c {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int N = in.nextInt();
            long[] A = new long[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextLong();
            }
            Arrays.sort(A);
            long sum = 0;
            long mod = 1000000007;
            for (int i = 0; i < N; i++) {
                for (int j = 0; j < N; j++) {
                    if (A[i] < A[j]) {
                        sum = (sum + ((A[i] * A[j]) % mod)) % mod;
                    }
                }
            }
            out.println(sum);
        }

    }
}