#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <iomanip>
using namespace std;
typedef long long LL;

int main(){
    LL N;
    cin >> N;
    LL M1 = (N+1) / 2;
    LL M2 = (N-1) / 2;
    cout << M1 * (M1-1) / 2 + M2 * (M2-1) / 2 << endl;
    return 0;
}