Author:  StdAlg  Time limit:  1 sec  
Input file:  input.txt  Memory limit:  256 Mb  
Output file:  output.txt 
You are to write a program that receives an unweighted undirected graph and writes all its vertices in order of increasing distance from given vertex S. Distance between vertices A and B is the length of the shortest path from A to B. If there are several vertices such that their distances to S are equal, they may be printed in arbitrary order.
Input file contains three integers N, M and S, where M is the number of edges, S is the starting vertex. Vertices are numbered with integer numbers from 1 to N. Each of next M lines contains a pair of integers — numbers of vertices connected by an edge.
Output file must contain sequence of vertex numbers sorted by increasing distance from S. If some vertex is not reachable from S, output a single number − 1.
No.  Input file (input.txt ) 
Output file (output.txt ) 

1 

