#include <iostream>
#include <algorithm>
using namespace std;
typedef long long int ll;
int main(){
	ll n;	cin>>n;
	ll ans=0;
	for(ll i=0;i<n;i++){
		ans=max(ans,(i+1)*(n-i+1));
	}
	cout<<ans-1<<endl;
	return 0;
}