write a go solution for Description:
There are n cities and m roads in Berland. Each road connects a pair of cities. The roads in Berland are one-way.

What is the minimum number of new roads that need to be built to make all the cities reachable from the capital?

New roads will also be one-way.

Input Format:
The first line of input consists of three integers n, m and s (1<=n<=5000,0<=m<=5000,1<=s<=n) — the number of cities, the number of roads and the index of the capital. Cities are indexed from 1 to n.

The following m lines contain roads: road i is given as a pair of cities u_i, v_i (1<=u_i,v_i<=n, u_inev_i). For each pair of cities (u,v), there can be at most one road from u to v. Roads in opposite directions between a pair of cities are allowed (i.e. from u to v and from v to u).

Output Format:
Print one integer — the minimum number of extra roads needed to make all the cities reachable from city s. If all the cities are already reachable from s, print 0.

Note:
The first example is illustrated by the following:

For example, you can add roads (6,4), (7,9), (1,7) to make all the cities reachable from s=1.

The second example is illustrated by the following:

In this example, you can add any one of the roads (5,1), (5,2), (5,3), (5,4) to make all the cities reachable from s=5.. Output only the code with no comments, explanation, or additional text.