#include<bits/stdc++.h>
using namespace std;
int n,ans=0;
void f(int x){
    for(int i=1;i<=x/2;i++){
        ans++;
        f(i);
    }
}
int main(){
    cin>>n;
    f(n);
    cout<<ans;
 
    return 0;
}
 

/**************************************************************
	Problem: 1307
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/