#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<map>
#include<cstring>
#include<stdlib.h>
#include<vector>
#include<stack>
#include<math.h>
#define ll long long
#define inf (0x3f3f3f3f)
#define mod (1000000007)
using namespace std;

ll a[61] = {0,1,2,3,5,8,12};


int main()
{
    for (int i = 6; i <= 60; i++)
        a[i] = a[i - 3] + a[i - 1] + 1;
    int n;
    while (scanf("%d", &n) != EOF)
        printf("%I64d\n", a[n]);
    return 0;
}