The Tribonacci numbers: T(0)=0, T(1)=1, T(2)=1, T(n)=T(n-1)+T(n-2)+T(n-3). Return T(n).
Example 1
Input: n = 4
Output: 4
Explanation: T(4) = 1 + 1 + 2 = 4.
Output: 4
Explanation: T(4) = 1 + 1 + 2 = 4.
Example 2
Input: n = 25
Output: 1389537
Explanation: The 25th Tribonacci number.
Output: 1389537
Explanation: The 25th Tribonacci number.