#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <cstdio>
using namespace std;
long long n,F[70][70];
int main()
{
    while(scanf("%I64d",&n)!=EOF)
    {
        memset(F,0,sizeof(F));
        F[1][1]=1;
        for(long long i=2;i<=n;i++)
        {
            for(long long j=1;j<=i;j++)
            {
                F[i][j]=F[i-1][j];
            }
            if(i>=4)
            {
                for(long long k=i-3;k>=1;k--)
                F[i][i]+=F[i-1][k];
            }
            F[i][i]+=1;
        }
        long long ans=0;
        for(long long j=1;j<=n;j++)
            ans+=F[n][j];
        printf("%I64d\n",ans);
    }
    return 0;
}