1 import java.util.*;  2 import java.awt.*; 3 import java.math.*; 4  5 public class Main { 6      7     public static void main(String args[]) { 8      Scanner cin=new Scanner(System.in); 9      int n, i;10      int f[] = new int[35];11      f[0] = 0;12      f[1] = 1;13      f[2] = 2;14      f[3] = 3;15      for(i = 4; i < 31; i ++)16          f[i] = f[i-1] + f[i-2] + f[i-3];17      while(cin.hasNext())  //多组18      {19          n  = cin.nextInt();20          System.out.println(f[n]);21      }22     }23 }