Calculating Function codeforces in c++

 A. Calculating Function

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

For a positive integer n let's define a function f:

f(n) =  - 1 + 2 - 3 + .. + ( - 1)nn

Your task is to calculate f(n) for a given integer n.

Input

The single line contains the positive integer n (1 ≤ n ≤ 1015).

Output

Print f(n) in a single line.

Examples

input

Copy

4

output

Copy

2

input

Copy

5

output

Copy

-3

Note

f(4) =  - 1 + 2 - 3 + 4 = 2

f(5) =  - 1 + 2 - 3 + 4 - 5 =  - 3

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soulution:

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Copy

#include<iostream>
using namespace std;
int main()
{
	long long n, sum;
	cin >> n;
	if (n % 2 == 0)
		sum = (n / 2);
	else
		sum = ((n + 1) / 2) * (-1);
	cout << sum << endl;
	return 0;
}