The Tribonacci sequence Tn is defined as follows:

T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.

Given `n`, return the value of Tn.

Example 1:

    Input: n = 4
    Output: 4
    Explanation:
    T_3 = 0 + 1 + 1 = 2
    T_4 = 1 + 1 + 2 = 4

Example 2:

    Input: n = 25
    Output: 1389537

Constraints:

- `0 <= n <= 37`
- The answer is guaranteed to fit within a 32-bit integer, ie. `answer <= 2^31 - 1`.