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 JavaScript (Node.js 12.16.1) (judge verdict: Wrong Answer)

function Main(input) {
    tmp = input.split("\n");
    n = parseInt(tmp[0], 10);
    a = tmp[1].split(" ").map(Number);
    MOD = 1000000007;
	result = 0;

    for (let i = 0; i < n; i++) {
                  
        for (let j = 1; j < n; j++) {
			num1 = a[i] % MOD;
            num2 = a[j] % MOD;

            if (i < j) {                
           		result += (num1  * num2) % MOD;
            	result = result % MOD
            }
        }        
    }
    
    console.log(result);

}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));