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