#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

const int Infinit = 10000000;
const int  NMAX = 200000;
priority_queue<pair<int, int>> pq;
vector<pair<int, int>>G[NMAX + 1];
int d[NMAX + 1], tata[NMAX + 1], viz[NMAX + 1];

ifstream f("apm.in");
ofstream g("apm.out");

int main() {
    int n, m;
    f >> n >> m;

    for (int i = 1; i <= m; i++) {
        int x, y, c;
        f >> x >> y >> c;
        G[x].push_back({y, c});
        G[y].push_back({x, c});
    }

    for (int i = 1; i <= n; i++) {
        d[i] = Infinit;
        viz[i] = 0;
    }

    d[1] = 0;
    pq.push({d[1], 1});
    int s = 0;

    while(!pq.empty()){
        int x = pq.top().second;
        pq.pop();

        if(viz[x]) {
            continue;
        }
        viz[x] = 1;
        s = s + d[x];

        for(auto next : G[x]){
            if(viz[next.first] == 0 && d[next.first] > next.second){
                d[next.first] = next.second;
                tata[next.first] = x;
                pq.push({d[next.first], next.first});
            }
        }
    }

    g << s << endl;
    for(int i = 2; i <= n; i++) {
        g << tata[i] << " " << i << endl;
    }
}