486A - Calculating Function.cpp

/*
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
inputCopy
4
outputCopy
2
inputCopy
5
outputCopy
-3
Note
f(4)?=??-?1?+?2?-?3?+?4?=?2

f(5)?=??-?1?+?2?-?3?+?4?-?5?=??-?3
*/



#include<bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    
    long long n;
    cin >> n;
    
    if (n % 2) {
    	cout << - (n + 1) / 2;
	} else cout << n / 2;
  
    

    return 0;
}