#include<bits/stdc++.h>
using namespace std;
int n,ans;
void  f(int x){
    for(int i=1;i<=x/2;i++){
        ans++;
        f(i);
    }       
}
int main(){
	cin>>n;
	f(n);
	cout<<ans;
}
/**************************************************************
	Problem: 1307
	User: linweilun
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/