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 Go (1.14.1) (judge verdict: Wrong Answer)

package main

import (
	"fmt"
)

func main() {
	var n, tmp int
    var a []int
	fmt.Scanf("%d", &n)
	for i := 0; i < n; i++ {
		fmt.Scanf("%d", &tmp)
      a = append(a, tmp)
	}
  
	sum := 0
	for i := 0; i < n; i++ {
        for j := 0; j < n; j++ {
            if a[i] >= a[j] {
              continue
            }
          	sum += a[i]*a[j]
        }
	    if sum > 1000000007{
          	sum = sum % 1000000007
        }
    }

	fmt.Printf("%d\n", sum)
}