#pragma comment(linker, "/STACK:1677721600")
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cmath>
#include <ctime>
#include <bitset>
#include <vector>
#include <cstdio>
#include <cctype>
#include <cstdarg>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
using namespace std;
#define INF 0x3f3f3f3f
#define inf (-((LL)1<<40))
#define root 1, 1, n
#define middle ((L + R) >> 1)
#define lson k<<1, L, (L + R)>>1
#define rson k<<1|1,  ((L + R)>>1) + 1, R
#define mem0(a) memset(a,0,sizeof(a))
#define mem1(a) memset(a,-1,sizeof(a))
#define mem(a, b) memset(a, b, sizeof(a))
#define FIN freopen("in.txt", "r", stdin)
#define FOUT freopen("out.txt", "w", stdout)
#define rep(i, a, b) for(int i = a; i <= b; i ++)
#define dec(i, a, b) for(int i = a; i >= b; i --)

//typedef __int64 LL;
typedef long long LL;
typedef pair<int, int> Pair;
const int MAXN = 300000 + 10;
const int MAXM = 1100000;
const double eps = 1e-12;
LL MOD = 1000000007;

LL f[MAXN], ans[MAXN];

void init(int n) {
    ans[1] = 1;
    ans[2] = 2;
    ans[3] = 3;
    f[1] = 1; f[2] = 1; f[3] = 1;
    rep (i, 4, n) {
        f[i] = 1;
        rep (j, 1, i - 3) f[i] += f[j];
        ans[i] = ans[i - 1] + f[i];
    }
}

int main()
{
#ifndef ONLINE_JUDGE
    FIN;// FOUT;
#endif
    init(60);
    int n;
    while(~scanf("%d", &n)) {
        cout << ans[n] << endl;
    }
    return 0;
}