SP5115 SPHIWAY - Two "Ways"

There are N places and M bidirectional way. No two places have more than one direct way. Ana wants to walk from S to T and return to S by a itinerary that satisfy: \- No way can be go twice. \- Length of itinerary is the minimum.

Line 1: 4 integers: N, M, S, T (N

Length of the itinerary if it exists. Else print -1.