#include <cstdio>
#include <iostream>
#include <algorithm>
#include <memory.h>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <cassert>
#include <ctime>
#include <bitset>
using namespace std;
typedef long long LL;
typedef pair<int, int> pii;
template<class T>
inline void chkmax(T& x, T y) {
    if (x < y) x = y;
}

template<class T>
inline void chkmin(T& x, T y) {
    if (y < x) x = y;
}
LL res[100];
int main() {
    int i;
    for (i = 1; i <= 3; i++) res[i] = i;
    for (i = 4; i <= 60; i++) res[i] = res[i - 1] + res[i - 3] + 1;
    int Tcase;
    int n;
    while (scanf("%d", &n) > 0) {
        printf("%I64d\n", res[n]);
    }
    return 0;
}