//vanitas vanitatum et omnia vanitas
#include<bits/stdc++.h>
#define fi first
#define se second
#define eb emplace_back
#define mp make_pair
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
template<typename T,typename U>
T ceil(T x, U y) {return (x>0?(x+y-1)/y:x/y);}
template<typename T,typename U>
T floor(T x, U y) {return (x>0?x/y:(x-y+1)/y);}
template<class T,class S>
bool chmax(T &a,const S b) {return (a<b?a=b,1:0);}
template<class T,class S>
bool chmin(T &a,const S b) {return (a>b?a=b,1:0);}
int popcnt(int x) {return __builtin_popcount(x);}
int popcnt(ll x)  {return __builtin_popcountll(x);}
int topbit(int x) {return (x==0?-1:31-__builtin_clz(x));}
int topbit(ll x)  {return (x==0?-1:63-__builtin_clzll(x));}
int lowbit(int x) {return (x==0?-1:__builtin_ctz(x));}
int lowbit(ll x)  {return (x==0?-1:__builtin_ctzll(x));}

#define int long long
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef tuple<int,int,int> tiii;
int read() {
  int x=0,w=1; char c=getchar(); 
  while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
  while(isdigit(c)) {x=x*10+(c-'0'); c=getchar();}
  return x*w;
}

const int N=505,inf=0x3f3f3f3f3f3f3f3f;
int w[N][N],n,m,ans,d[N][N],dep[N],fr[N][N],vst[N],tp;
vi e[N];
vp anst;

void dfs(int u,int fa) {
  for(int v:e[u]) if(v!=fa) dep[v]=dep[u]+w[u][v], dfs(v,u);
  if(dep[u]>dep[tp]) tp=u;
}
void dijkstra(int c,int *fr,int *d) {
  rep(i,0,n) d[i]=inf, vst[i]=0; d[c]=0, fr[c]=0;
  rep(t,1,n) {
    int u=0; rep(i,1,n) if(!vst[i]&&d[i]<d[u]) u=i; vst[u]=1;
    rep(v,1,n) if(chmin(d[v],d[u]+w[u][v])) fr[v]=u;
  }
}
void work(int x,int y) {
  rep(i,1,n) e[i].clear(), dep[i]=0;
  int m1=0,m2=0;
  rep(i,1,n) chmax(m1,d[x][i]), chmax(m2,d[y][i]);
  ld a=(m1-m2+w[x][y])/2.;
  rep(i,1,n) if(i!=x&&i!=y) {
    int fa=(d[x][i]+a<d[y][i]+w[x][y]-a?fr[x][i]:fr[y][i]);
    if(fa) e[fa].eb(i), e[i].eb(fa);
  } if(x!=y) e[x].eb(y), e[y].eb(x);
  dep[x]=0, tp=x; dfs(x,0); int s=tp; tp=s;
  rep(i,1,n) dep[i]=0; dfs(s,0); int t=tp;
  if(chmin(ans,dep[t])) {
    anst.clear();
    rep(i,1,n) for(int j:e[i]) if(i<j) anst.eb(i,j);
  }
}

signed main() {
  n=read(), m=read(), ans=inf;
  rep(i,1,n) rep(j,1,n) w[i][j]=inf;
  rep(i,1,m) {
    int u=read(), v=read(), x=read();
    w[u][v]=w[v][u]=x;
  } rep(i,1,n) w[i][i]=0;
  rep(c,1,n) dijkstra(c,fr[c],d[c]);
  rep(x,1,n) rep(y,x,n) if(w[x][y]!=inf) work(x,y);
  printf("%lld\n",ans);
  for(auto [x,y]:anst) printf("%lld %lld\n",x,y);
  return 0;
}