#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <iomanip>
using namespace std;
#define INF 1e9
#define PI acos(-1)
typedef long long ll;



int main() {
	int d; cin >> d;
	int ans = 0;

	for (int i = 1; i <= 10000; i++) {
		for (int j = 1; j <= 10000; j++) {
			if (2 * (i + j) > d)continue;
			ans = max(ans, i*j);
		}
	}

	cout << ans << endl;

	return 0;
}