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

int main()
{
    freopen("pthuong.inp","r",stdin);
    freopen("pthuong.out","w",stdout);
    ll n, k, res;
    cin>>n;
    k = n/2;
    res = k*k;
    if (n%2==0)
        res =res-k;
    cout<<res;
    return 0;
}
