G. Irreversible Events
time limit per test
1.25 seconds
memory limit per test
1024 megabytes
input
standard input
output
standard output
Example
Input
3
3 2
1 2
2 3
4 3
1 2
2 3
1 3
6 7
4 2
4 1
1 2
2 3
3 1
5 6
3 6
Output
0
1
2