#include<map>
#include<set>
#include<stack>
#include<queue>
#include<cmath>
#include<vector>
#include<cstdio>
#include<string>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#define inf 0x0f0f0f0f
#define LL long long
#define eps 1e-8
using namespace std;

const int maxn = 61+10;
LL dp[maxn][maxn];
void init()
{
    memset(dp , 0 ,sizeof dp);
    for (int i=1;i<=60;i++)
    {
        dp[i][1]=1; dp[i][2]=1; dp[i][3]=1;
        for (int j=4;j<=i;j++)
        {
            for (int k=1;k<=j-3;k++) dp[i][j]+=dp[i][k];
            dp[i][j]++;
        }
    }
}
int main()
{
    init();
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        LL ans=0;
        for (int i=1;i<=n;i++) ans+=dp[n][i];
        printf("%I64d\n",ans);
    }
    return 0;
}