using System;

​

 public class Tribonacci

 {

  private const long Mod = 1000000007;

​

  public static long TribonacciRecursive(long n)

  {

  if (n == 0)

  {

  return 0;

  }

  if (n == 1 || n == 2)

  {

  return 1;

  }

​

  return (TribonacciRecursive(n - 1) + TribonacciRecursive(n - 2) + TribonacciRecursive(n - 3)) % Mod;

  }

​

  public static class TestTribonacci

  {

  public static bool RunTests()

  {

  bool allTestsPassed = true;

​

  allTestsPassed &= Test(0, 0, "Test Case 0");

  allTestsPassed &= Test(1, 1, "Test Case 1");

  allTestsPassed &= Test(2, 1, "Test Case 2");

  allTestsPassed &= Test(3, 2, "Test Case 3");

  allTestsPassed &= Test(4, 4, "Test Case 4");

  allTestsPassed &= Test(5, 7, "Test Case 5");

  allTestsPassed &= Test(6, 13, "Test Case 6");

  allTestsPassed &= Test(7, 24, "Test Case 7");

​

  if (allTestsPassed)

  {

  Console.WriteLine("All tests passed!");

  }

  else

  {

  Console.WriteLine("Some tests failed.");

  }

​

  return allTestsPassed;

  }

​

  private static bool Test(long n, long expected, string testName)

  {

  long actual = TribonacciRecursive(n);

  bool passed = actual == expected;

​

  Console.WriteLine($"{testName}: Expected {expected}, Actual {actual}, Passed: {passed}");

  return passed;

  }

  }

​

  public static void Main(string[] args)

  {

  // Example usage:

  long n = 10;

  long result = TribonacciRecursive(n);

  Console.WriteLine($"Tribonacci({n}) = {result}");

​

  // Run tests:

  TestTribonacci.RunTests();

  }

 }