Please someone explain sample test case. I don't understand how we can push flow 2 through 1->2 (output shows that) if in the input there is flow capacity 1? In the second line of the input there is
2 1 1 1, 3 1 1 3.
that means there is pipeline between 1 and 2 with max flow 1, but there is already 1 flow, so we can't push anything more or something else...?

Thank you in advance.

read carefully what "d" means.