#include <iostream>
using namespace std;

int main() {

    int n;
    cin >> n;
    int sum = 0;

    // write your code here......
    if (n % 2 != 0)
    {
        --n;
        sum = (n + 2) / 2 * n / 2;
    }
    else
    {
        sum = (n + 2) / 2 * n / 2;
    }
    cout << sum << endl;

    return 0;
}