#include<iostream> using namespace std; int main(){ int,a[100],n; unsigned long long a[100]; a[1]=1; a[2]=2; a[3]=4; a[4]=7; while(cin>>n); for(i=4;i<=n;i++); a[i]=a[i-3]+a[i-2]+a[i-1]; cout<<a[n]<<endl; return 0; }