#include <iostream>
#include <fstream>
using namespace std;

ifstream in("fractii.in");
ofstream out("fractii.out");
int main(){
    int n, s = 0;
    in>>n;
    if(n % 2 == 0){
        s = ((n - 1) * (n / 2)) + ((n / 2) * (n / 2));
        out<<s + 1;
    }
    else{
        s = ((n - 1) * (n / 2 + 1)) + ((n / 2 + 1) * (n / 2));
        out<<s + 1;
    }
    return 0;
}