#include <stdio.h>

int Tribonacci(int n){
    if(n >= 3){
        return Tribonacci(n - 1) + Tribonacci(n - 2) + Tribonacci(n - 3);
    } else if (n == 1 || n == 2){
        return 1;
    } else {
        return 0;
    }
}

int main() {
    int x, trib;
    scanf("%d", &x);

    trib = Tribonacci(x);
    printf("%d", trib);
  }