Points: 5
Time limit: 1.0s
Java 2.0s
Memory limit: 128M
PyPy 3 256M

Author:
Problem type

On Zeyu'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 Zeyu is bad at math, he wants you to write a program which will solve the problem for him.

Input Specification

On the first line, Zeyu will tell you $$N$$, the number of integers.

On the next line, Zeyu 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

$$1 \le N \le 10^6$$

$$-10^5 \le {a_i} \le 10^5$$

$$1 \le N \le 10^3$$

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