#include <iostream>

using namespace std;

int countWays(int);

int main()
{
   int ways, stairs;

   cout << "enter number of stairs: ";
   cin >> stairs;

   ways = countWays(stairs);

   cout << ways << endl;

   return 0;
}

int countWays(int numStairs)
{
   if(numStairs == 1)
   {
      return 1;
   }
   else if(numStairs == 0)
   {
      return 0;
   }
   else
   {
      return countWays(numStairs -1) + countWays(numStairs - 2) + countWays(numStairs -2);
   }
}