#include<bits/stdc++.h>
using namespace std;
int n,ans;
void f(int x){
    for(int i=1;i<=x/2;i++){
    	ans+=1;
			f(i);
	}
}
int main(){
   		cin>>n;
   		f(n);
   	 	cout<<ans;
    return 0;
}
/**************************************************************
	Problem: 1307
	User: wuzhijing
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/