#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
using namespace std;
typedef long long int ll;
using ull = unsigned long long;


int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll n; cin >> n;
    ll res=0;
    for(ll i=1;i<n;i++){
        res=max(res,(i+1)*(n-i+1));
        //cout << (i+1)*(n-i+1) << endl;
    }
    printf("%lld\n",res-1);
}