#include<bits/stdc++.h>
using namespace std;
int ways(int x);
int main()
{
int x;
cin>>x;
cout<<ways(x)<<endl;
return 0;
}

int ways(int x)
{
if(x==1)
return 1;
else
{
if(x==2)
return 2;
else
{
if(x==3)
return 4;
else
return ways(x-1)+ways(x-2)+ways(x-3);
}
}
}