#include<bits/stdc++.h>
using namespace std;
long long n,a[1005];
int main(){
    cin>>n;
    a[1]=1;
    a[2]=2;
    for(int i=3;i<=n;i++){
    	a[i]=a[i-1]*2+a[i-2];
	}
	cout<<a[n];
	return 0;
}

/**************************************************************
	Problem: 1369
	User: chenjingqi
	Language: C++
	Result: Wrong Answer
****************************************************************/