#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <cmath>
#include <iomanip>
#include <map>
using namespace std;
typedef long long LL;

const LL MOD=1000000000;

int main(){
    LL D;
    cin >> D;
    LL ans = 0;
    for(int i = 0; i*2 <= D; i++){
        int j = (D-i*2) / 2;
        ans = max<LL>(ans, i*j);
    }
    cout << ans << endl;
    return 0;
}