include <bits/stdc++.h>

using namespace std;

int main() {

unsigned long long F[75] = {0, 1, 2, 4};
for (int i = 4; i <= 73; i++)
	F[i] = F[i - 3] + F[i - 2] + F[i - 1];
for (int n; scanf("%d", &n) != EOF;)
	printf("%llu\n", F[n]);
return 0;

}