//#include <必AC>

include <bits/stdc++.h>

using namespace std; unsigned long long a[80]; int main(){

int t;
a[1] = 1;
a[2] = 2;
a[3] = 4;
for(int i = 4; i <= 73; i++){
	a[i] = a[i - 3] + a[i - 2] + a[i - 1];
}
while(cin >> t){
	cout << a[t] << endl;
}
return 0;

}