#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define ps push
#define in insert
#define f first
#define s second
#define nl cout<<"\n"
#define ca(v) for(auto i:v) cout<<i<<" ";
#define cbit(x) __builtin_popcount(x)
#define gcd(a, b) __gcd(a, b)
#define lcm(a, b) (a*b/gcd(a, b))
const int xm[4] = {-1, 1, 0, 0};
const int ym[4] = {0, 0, -1, 1};
const int MOD = 1e9 + 7;
const int MAXN = 2e3 + 5;
const ll POW = 9973;

struct ed {
    int u, v, w, id;
    friend bool operator<(ed a, ed b) {
        return a.w < b.w;
    }
};

vector<ed> adj[MAXN];

vector<ed> path;
bool dfs(int x, int p, int g) {
    if(x == g) return 1;
    for(auto e:adj[x]) {
        int a = e.u;
        if(a == x) a = e.v;
        if(a == p) continue;
        path.pb(e);
        if(dfs(a,x,g)) return 1;
        path.pop_back();
    }
    return 0;
}

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    if (fopen("input.in", "r")) {
        freopen("input.in", "r", stdin);
        freopen("output.out", "w", stdout);
    }

    int n, m;
    cin>>n>>m;
    vector<ed> eds;
    vector<ed> ord;
    set<int> active;
    

    for(int i=0; i<m; i++) {    
        int u, v, w;
        cin>>u>>v>>w;
        u--; v--;
        eds.pb({u,v,w,i});
        ord.pb(eds.back());
    }
    for(int i=0; i<n-1; i++) active.in(i);
    vector<pair<int, int>> res; 
    sort(all(ord));
    for(auto e:ord) {
        if(e.id < n-1) continue;
        for(int i=0; i<m; i++){
            if(active.find(i) != active.end()) {
                adj[eds[i].v].pb(eds[i]);
                adj[eds[i].u].pb(eds[i]);
            }
        }
        dfs(e.u, -1, e.v);
        sort(all(path));
        if(path.back().w > e.w) {
            res.pb({path.back().id, e.id});
            if(active.find(path.back().id) == active.end()) return 0;
            assert(active.find(path.back().id) != active.end());
            active.erase(active.find(path.back().id));
            active.insert(e.id);
        }

        for(int i=0; i<n; i++) adj[i].clear();
        path.clear();
    }
    cout<<res.size()<<"\n";
    for(auto p:res) cout<<p.f+1<<" "<<p.s+1<<"\n";

}

answer.code: In function ‘int main()’:
answer.code:53:16: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   53 |         freopen("input.in", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
answer.code:54:16: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   54 |         freopen("output.out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/13/string:43,
                 from /usr/include/c++/13/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:52,
                 from answer.code:4:
/usr/include/c++/13/bits/allocator.h: In destructor ‘std::_Vector_base<ed, std::allocator<ed> >::_Vector_impl::~_Vector_impl()’:
/usr/include/c++/13/bits/allocator.h:184:7: error: inlining failed in call to ‘always_inline’ ‘std::allocator< <template-parameter-1-1> >::~allocator() noexcept [with _Tp = ed]’: target specific option mismatch
  184 |       ~allocator() _GLIBCXX_NOTHROW { }
      |       ^
In file included from /usr/include/c++/13/vector:66,
                 from /usr/include/c++/13/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:53:
/usr/include/c++/13/bits/stl_vector.h:133:14: note: called from here
  133 |       struct _Vector_impl
      |              ^~~~~~~~~~~~