#include<bits/stdc++.h>
using namespace std;
int n,h=0;
int f(int s){
	if(s==1) return 0;
	if(s==2) return 1;
	else return f(s-1)*(f(s-1)+f(s-2));
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		h=h+f(i);
	}
	cout<<h; 
    return 0;
}
/**************************************************************
	Problem: 1694
	User: panyuchen
	Language: C++
	Result: Wrong Answer
****************************************************************/