You are to write a program that receives a weighted undirected graph and finds length of its shortest spanning tree.
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 next M lines contain three
integers describing an edge — numbers of vertices, connected by an edge and its weight respectively. All weights are
positive. There is at most one edge connecting two vertices.
Output file format
Output file must contain a signle integer number — length of the SST. If it is impossible to construct spanning tree,
output file must contain −1.