#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std ;
const int maxn =110 ;
typedef __int64 ll ;
ll dp[maxn][2] ;
int main()
{
    dp[1][0] = 0;
    dp[1][1] = 1 ;
    dp[2][0] = 1;
    dp[2][1] = 1 ;
    dp[3][0] = 2;
    dp[3][1] = 1 ;
    for(int i = 4;i <= 60;i++)
    {
        int sum = 0 ;
        dp[i][1] = dp[i-3][1] + dp[i-3][0] + 1 ;
        dp[i][0] = dp[i-1][1] + dp[i-1][0] ;
    }
    int n ;
    while(~scanf("%d" ,&n))
    {
        printf("%I64d\n"  ,dp[n][0] + dp[n][1]) ;
    }
}