You are to write a program that receives an undirected connected graph and finds its Eulerian cycle.
Input file format
Input file contains two integers N, M.
Vertices are numbered with integer numbers from 1 to N. M is the number of edges. Each of following M lines contains a pair of
vertex numbers, connected by some edge. There is at most one edge connecting two vertices.
Output file format
Output file must contain a sequence of vertex numbers in order of traversal in an Eiler cycle.
If there does not exist any Eiler cycle, output file must contain −1.
