Codeforces 486 - A problem solution

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

4

output

2

input

5

output

-3

Note

f(4) =  - 1 + 2 - 3 + 4 = 2

f(5) =  - 1 + 2 - 3 + 4 - 5 =  - 3

Problem link : https://codeforces.com/problemset/problem/486/A

Solution :

• [tab]
• C++

• #include<bits/stdc++.h>
  using namespace std;
  int main()
  {
      long long n;
      cin>>n;
      if(n%2==0)
      {
          cout<<n/2<<endl;
      }
      else
      {
          cout<<-(n+1)/2;
      }
      return 0;
  }