C++ :

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <cassert>
#include <complex>
#include <ctime>

#define clr(x,a) memset(x,a,sizeof(x))
#define sz(x) (int)x.size()
#define rep(i,n) for(int i=0;i<n;i++)
#define repeat(i, a, b) for(int i=(a);i<=(b);i++)
#define all(v) (v).begin(), (v).end()
#define Unique(store) store.resize(unique(store.begin(),store.end())-store.begin())
#define X first
#define Y second



using namespace std;
const int N=123456+10;

int main () {
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
   int n;
   while (cin>>n) {
        int ret;
        if (n%2==0) {
            ret=n/2;
        }
        else {
            ret=n/2-n;
        }
        cout<<ret<<endl;
    }
    return 0;
}

Java :

import java.util.Scanner;
public class Main
{
	static Scanner inputScanner=new Scanner(System.in);
	public static void main(String[] argsStrings)
	{
		while(inputScanner.hasNextInt())
		{
			int n=inputScanner.nextInt();
			if (n%2==0)
				System.out.println(n/2);
			 else
				 System.out.println(-(n+1)/2);
		}
	}
}