#include <iostream>
using namespace std;

int main() {
    int n;
    cin>>n;
    int sum=0;
    for(int i=1;i<=n;++i){
        if(i%2==1){
            sum+=i;
        }else{
            sum-=i;
        }
    }
    cout<<sum<<endl;
    return 0;
    }