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

ifstream ci("nunta.in");
ofstream cou("nunta.out");

int n;

void rez(){
    int k;
    if(n%2==0){
        k=n/2;
        cou<<k*(k+1)/2+1;
    }else{
        k=n/2+1;
        cou<<k*(k+1)/2;
    }
}

int main()
{
    ci>>n;
    rez();
    return 0;
}