#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e6+5;
int n;
int ans;
signed main(){
	cin>>n;
	if(n==1)cout<<"ovo";
	else if(n<=4)cout<<0;
	else{
		int k=ceil(double(n-4)/2);
		cout<<k;
	}
}