Link to problem: http://mirror.codeforces.com/problemset/problem/505/D

My submission: http://mirror.codeforces.com/contest/505/submission/18861557

My idea is to count the amount of sub-trees of the graph that doesn't contain a cycle, and the answer would be n-(amount of sub-trees without a cycle). However my code fails on the test case 6 and I have no idea how did the test case got me... Can anyone point out the flaw of my code or even my approach on solving this problem?