#include<bits/stdc++.h>
using namespace std;
int ans=-1;
void dfs(int m){
    int i;
    ans++;
    for(i=1;i<=m/2;i++)
        dfs(i);
}
int main(){
    int n;
    cin>>n;
    dfs(n);
    cout<<ans-1+1;
}
/**************************************************************
	Problem: 1307
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/