Passing news by DM

There are n users on a social network, numbered from 0 to n - 1. A record [a, b] in follows means that a follows b. On this social network, you can send a DM only to people you follow.

Person start wants to pass some news to person target. Anyone who receives the news by DM can pass it on by DM. Complete the function solution, which returns the smallest number of DMs that must be sent for the news to reach target. If the news cannot reach target, return -1.

Function

solution(n, follows, start, target)

Constraints

• n is an integer from 2 to 100,000.
• The length of follows is from 1 to 100,000.
• Each element of follows has the form [a, b], where a and b are different integers from 0 to n - 1. The same record never appears twice.
• start and target are different integers from 0 to n - 1.

Examples

Starter code

def solution(n, follows, start, target):
    answer = 0
    return answer