#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
const int N=70;
int a[N];
int main(){
    int n;
    cin>>n;
    a[0]=1,a[1]=1,a[2]=2;
    for(int i=3;i<=n;i++) a[i]=a[i-1]+a[i-2]+a[i-3];
    cout<<a[n]<<endl;
    return 0;
}