#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <stack>

using namespace std;
int noduri, muchii;
vector<pair<int,int>> graf[500000],apm;
int vizitat[500000];
int costTotal;
ifstream f("apm.in");
ofstream g("apm.out");
priority_queue<pair<int,pair<int,int> > > coada;
//coada cu cost si muchii
int parinte[500000];
int distanta[500000];
void citire()
{
    f>>noduri>>muchii;
    for(int i=0;i<muchii;i++)
    {
        int x,y,c;
        f>>x>>y>>c;
        graf[x].push_back({y,c});
        graf[y].push_back({x,c});
    }
}
void Prim()
{
    //nodul de start este 1, cu tatal 0 si cost 0
    coada.push({0,{1,0}});
    while(!coada.empty())
    {
        int cost = coada.top().first;
        int nodCurent = coada.top().second.first;
        int nodParinte = coada.top().second.second;
        coada.pop();
        if(vizitat[nodCurent] != 0)
            continue;
        costTotal -= cost;
        if(nodParinte)
            apm.push_back({nodParinte,nodCurent});
        if(vizitat[nodCurent] == 0)
        {
            // bag toate muchiile
            for(auto pereche: graf[nodCurent])
            {
                int vecin = pereche.first;
                int cost = pereche.second;
                if(vizitat[vecin] == 0)
                    coada.push({-cost,{vecin,nodCurent}});
            }
            vizitat[nodCurent] = 1;
        }
    }
}
int main()
{
    citire();
    Prim();
    g<<costTotal;
    for(auto pereche: apm)
    {
        g<<pereche.first<<" "<<pereche.second<<"\n";
    }
    return 0;
}