#include <algorithm>
#include <iostream>
#include <iomanip>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

#define FOR(i,s,e) for (int i = int(s); i < int(e); i++)
#define FORIT(i,c) for (typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define ISEQ(c) (c).begin(), (c).end()

int SURP = 1000000007;

int main(){
	int n;
	cin >> n;
	int a = (n+1)/2;
	long long int cnt = 0;
	FOR(i,2,a+1){
		long long int l = 2 * i - 1;
		cnt += n - l + 1;
	}
	cout << cnt << endl;
	return 0;
}