## Problem BJ. SST for sparse graph ≡

 Author: StdAlg Time limit: 1 sec Input file: input.txt Memory limit: 10 Mb Output file: output.txt

### Statement

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.

### Constraints

1 ≤ N, M ≤ 100000 All weights are less or equal 1000.

### Sample tests

No. Input file (input.txt) Output file (output.txt)
1
3 3
1 2 10
2 3 10
3 1 10
20

0.171s 0.093s 15