## Zeyu and Addition

Submit solution

Points:
5

Time limit:
1.0s

Java
2.0s

Memory limit:
128M

PyPy 3
256M

Author:

Problem type

On

's first day at math class, the professor gives him a sequence of \(N\) integers \({a_i, a_2, …, a_N}\). The professor asks him for the sum of all pairs \((a_i, a_j)\), such that \(1 \le i,j \le N\). Since is bad at math, he wants you to write a program which will solve the problem for him.#### Input Specification

On the first line,

will tell you \(N\), the number of integers.On the next line,

will give you \(N\) space separated integers; \(a_1, a_2, ... a_N\)#### Output Specification

The sum of all pairs \((a_i, a_j)\) such that \(1 \le i,j \le N\). To prevent overflow, Java and C++ users are recommended to use the `long`

or `long long`

datatype, instead of `int`

.

#### Constraints

For all subtasks:

\(1 \le N \le 10^6\)

\(-10^5 \le {a_i} \le 10^5\)

##### Subtask 1 [40%]

\(1 \le N \le 10^3\)

##### Subtask 2 [60%]

No additional constraints.

#### Sample input

```
4
1 2 3 7
```

#### Sample Output

`104`

## Comments