#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <vector>
#include <queue>
#include <iostream>
#include <cassert>
#include <bitset>
#include <ctime>

using namespace std;

typedef long long LL;
typedef double DB;
typedef pair<int, int> PII;
typedef vector<int> VI;

#define X first
#define Y second
#define pb push_back

template<class T>
inline void chkmin(T &x, T y) {
    if (y < x) x = y;
}

template<class T>
inline void chkmax(T &x, T y) {
    if (x < y) x = y;
}

int n;
LL val[65];

int main() {
    
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);
    
    int i, j, k;
    
    val[0] = 1;
    val[1] = 1;
    val[2] = 2;
    val[3] = 3;
    for (i = 4; i <= 60; i++) {
        val[i] = val[i - 1] + val[i - 3] + 1;    
    }
    while (scanf("%d", &n) == 1) {
        cout << val[n] << endl;
    }
    
    return 0;    
}