http://e-maxx.ru/algo/connected_components
You need to output number of components minus 1.
Tests:

4 4 0
3 4
1 2
3 1
2 4
0


1 0 0
0

6 0 0
5

6 5 1
1 2
1 4
2 5
3 6
4 5
1 2
1

6 5 0
1 2
1 4
2 5
3 6
4 5
1

6 3 4
1 2
2 3
4 5
2

6 4 0
1 3
3 4
4 6
5 6
1

Edited by author 04.11.2020 21:20