#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <cmath>

using namespace std;

const int maxn = 80;

long long vis[maxn];
void init() {
    vis[1] = 1;
    vis[2] = 2;
    vis[3] = 3;
    vis[4] = 5;
    for(int i = 5; i <= 65; i++) {
        vis[i] = vis[i-1]+vis[i-3]+1;
    }
}
int main() {
    int n;
    init();
    while(~scanf("%d", &n)) {
        printf("%I64d\n", vis[n]);
    }
}