#include <iostream>
#include <algorithm>

using namespace std;

// f(n,lower)
long long maxNumber(long long n, long long lower) {
	long long upper = n - lower;
	return (lower + 1) * upper + lower;
}

int main() {
	long long n;
	cin >> n;
	// x: df(n,x)/dx=0
	long long floorMinArgX = n / 2;
	long long ceilMinArgX = (n + 1) / 2;
	long long floorMax = maxNumber(n, floorMinArgX);
	long long ceilMax = maxNumber(n, ceilMinArgX);
	cout << max(floorMax, ceilMax) << endl;
	return 0;
}