#include <algorithm>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#define rep(i, n) for (int i=0; i<n; ++i)
#define FOR(i, a, b) for (int i=a; i<b+1; ++i)
#define pb(x) push_back(x)
#define ll long long
#define debug(x) cout  << #x << " : " << x << endl;
using namespace std;

const int inf =1500000000;
int main () {
	int l;
	cin>>l;
	unsigned long long cnt=0;
	for (int i= 3; i <= l; i += 2) {
		cnt += l - (i - 1);
	}
	cout << cnt << endl;
	return 0;
}