#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#include<stack>
#include<queue>
#include<list>
#include<bitset>
#include<functional>

#define FOR(i, a, b) for(int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000
#define PI 3.14159265358979

using namespace std;
typedef pair<int, int> P;

int main(void) {
	int l;

	cin >> l;

	cout << (l - 1)*(l - 1) / 4 << endl;
	return 0;
}