#include<bits/stdc++.h>
using namespace std;
int total = 0;
void fun(int n, char* str)
{
    if(n==0)
    {
        char* p1 = strstr(str,"111");
        if(p1 == NULL)
        {
            total++;
        }
    }
    else{
        str[n-1]='1';
        fun(n-1,str);
        str[n-1]='0';
        fun(n-1,str);
        }
}
  
int main()
    {
        char str[41]={0};
        int n;
        scanf("%d",&n);
        fun(n,str);
        cout<<total<<endl;
    }


/**************************************************************
	Problem: 1689
	User: wengsihan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/