#include<bits/stdc++.h>
using namespace std;
int n,h;

void f(int x){
	for(int i=1;i<=x/2;i++){
		h++;
		f(i);
	}
}

int main(){
	cin>>n;
	f(n);
	cout<<h;
	return 0;
}

/**************************************************************
	Problem: 1307
	User: zengyixuan
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/