#include<bits/stdc++.h>

typedef long long ll;
typedef std::pair<int,int> pii;
const int MAXN = 6011;
struct edge{int v,w,nxt;}e[MAXN<<1|1];
int cnt=1,last[MAXN];
bool del[MAXN];
void adde(int u,int v,int w)
{
    e[++cnt].v=v,e[cnt].w=w, e[cnt].nxt=last[u],last[u]=cnt;
}

int n,m;
struct one
{
    int u,v,w,dex;
    bool operator< (const one& you)const
    {
        return w<you.w;
    }
}pre[MAXN],now[MAXN];
int fa[MAXN],fw[MAXN], dep[MAXN];
int exchange[MAXN];
void dfs(int u)
{
    //printf("dfs %d\n",u);
    for(int i=last[u];i;i=e[i].nxt)
    {
        if(del[i>>1])continue;
        int v=e[i].v;
        if(fa[u]==v)continue;
        fa[v]=u,fw[v]=i>>1, dep[v]=dep[u]+1;
        //printf("Fw[%d]=%d\n",v,fw[v]);
        dfs(v);
    }
}
bool less(int a,int b)
{
    //printf("Less %d %d ;%d %d\n",a,e[a<<1].w,b,e[b<<1].w);
    if(e[a<<1].w<e[b<<1].w)return 1;
    if(e[a<<1].w>e[b<<1].w)return 0;
    return (a<=n-1) && (b>n-1);
}
int get(int u,int v)
{
    //printf("Get (%d,%d)\n",u,v);
    if(dep[u]>dep[v])std::swap(u,v);
    int dex=0;
    while(dep[u]!=dep[v])
    {
        //printf("v=%d,fw=%d\n",v,fw[v]);
        if(less(dex,fw[v]))dex=fw[v];
        v=fa[v];
    }
    while(u!=v)
    {
        if(less(dex,fw[v]))dex=fw[v];
        v=fa[v];
        if(less(dex,fw[u]))dex=fw[u];
        u=fa[u];
    }
    //printf("dex=%d\n",dex);
    return dex;
}

void update()
{
    memset(dep,0,sizeof dep),memset(fa,0,sizeof fa),memset(fw,0,sizeof fw);
    dep[1]=1,dfs(1);
}
int pos[MAXN];
std::vector<pii>seq;
int main()
{
    scanf("%d%d",&n,&m);
    m-=n-1;
    for(int i=1;i<=n-1;++i)
    {
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        adde(u,v,w),adde(v,u,w);
        exchange[i]=i,pos[i]=i;
    }
    for(int i=1;i<=m;++i)scanf("%d%d%d",&now[i].u,&now[i].v,&now[i].w),now[i].dex=n-1+i;
    std::sort(now+1,now+m+1);
    int ans=0;
    update();
    for(int i=1;i<=m;++i)
    {
        pos[n-1+i]=now[i].dex;
        int w=now[i].w;
        int p=get(now[i].u,now[i].v);
        int pw=e[p<<1].w;
        //printf("i=%d,w=%d,p=%d,pw=%d\n",i,w,p,pw);
        if(pw>w)
        {
            del[p]=1;
            adde(now[i].u,now[i].v,w);
            adde(now[i].v,now[i].u,w);
            update();
            exchange[now[i].dex]=exchange[pos[p]];
            exchange[pos[p]]=0;
        }
        else cnt+=2;
    }
    for(int i=1;i<=m;++i)
        if(exchange[n-1+i])seq.emplace_back(pii(exchange[n-1+i],n-1+i));
    printf("%d\n",int(seq.size()));
    for(auto [x,y]:seq)printf("%d %d\n",x,y);
    return 0;
}