#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>

using namespace std;

int main()
{	
	long n;
	cin>>n;

	unsigned long long res=n-1;

	for(long i=1;i<=n/2;i++){
		res=max(res,(unsigned long long)(i+1)*(n-i+1));
	}

	cout<<res-1<<endl;

	return 0;

}