題目←

吐槽下考場上的魔改題面……
看出來是運輸計劃後，記得以前聽說過是二分，於是開始摸魚……
不會樹鏈剖分，考場上卡掉一個點
儘管實現步驟很麻煩，但思路清晰的話，具體打起來還是比較容易的一道題
能摸出來大概是人品比較好……

#include<iostream>
#include<cstdio>
#include<algorithm>
#define LL long long
using namespace std;
const LL MAXN = 300000 + 50;
struct edge{
    LL f,t,v;
}l[MAXN << 1
 
];
struct zt{
    LL f,t;
    LL v;
    LL lca;
}e[MAXN];
LL head[MAXN],next[MAXN << 1],tot;
void init(LL n){
    for(LL i = 1;i <= n;i ++){
        head[i] = -1;
    }
}
void build(LL f,LL t,LL v){
    l[++ tot] = (edge){f,t,v};
    next[tot] = head[f];
    head[f] = tot;
}
LL n,m,a,b,c;
LL deep[MAXN],fa[MAXN][26
 
];
LL ru[MAXN];
LL rank[MAXN];
void dfs(LL p,LL f){
    for(LL i = 1;i <= 25;i ++){
        fa[f][i] = fa[fa[f][i - 1]][i - 1];
    }
    for(LL i = head[f];i != -1;i = next[i]){
        LL t = l[i].t;
        if(t == p)continue;
        ru[t] ++;
        deep[t] = deep[f] + 1;
        fa[t][0] = f;
        rank[t] = rank[f] + l[i].v;
        dfs(f,t);
    }
}
LL LCA(LL a,LL b){
    if
 
(deep[a] < deep[b])swap(a,b);
    LL t = deep[a] - deep[b];
    for(LL i = 0;i <= 25;i ++){
        if(t & (1 << i)){
            a = fa[a][i];
        }
    }
    if(a == b)return a;
    for(LL i = 25;i >= 0;i --){
        if(fa[a][i] != fa[b][i]){
            a = fa[a][i];
            b = fa[b][i];
        }
    }
    return fa[a][0];
}
LL topo[MAXN];
LL L = 1,R = 1;
void toposort(){
    topo[R ++] = 1;
    while(L != R){
        LL u = topo[L];
        for(LL i = head[u];i != -1;i = next[i]){
            LL t = l[i].t;
            ru[t] --;
            if(!ru[t])topo[R ++] = t;
        }
        L ++;
    }
}
LL mid;
LL cf[MAXN];
bool check(LL x){
    LL cnt = 0;
    LL maxx = 0;
    for(LL i = 0;i <= n;i ++){
        cf[i] = 0;
    }
    for(LL i = 1;i <= m;i ++){
        if(e[i].v > x){
            cf[e[i].f] ++;
            cf[e[i].t] ++;
            cf[e[i].lca] --;
            cf[fa[e[i].lca][0]] --;
            cnt ++;
            maxx = max(maxx,e[i].v);
        }
    }
    for(LL j = n;j >= 1;j --){
        LL u = topo[j];
        for(LL i = head[u];i != -1;i = next[i]){
            LL t = l[i].t;
            if(deep[t] < deep[u])continue;
            cf[u] += cf[t];
        }
    }
    for(LL u = 1;u <= n;u ++){
        if(cf[u] < cnt)continue;
        for(LL i = head[u];i != -1;i = next[i]){
            if(deep[l[i].t] < deep[u])continue;
            if(cf[l[i].t] >= cnt){
                if(maxx - l[i].v <= x)return true;
            }
        }
    }
    return false;
}
void solve(){
    R ++;
    L --;
    while(R - L > 1){
        mid = L + R >> 1;
        if(check(mid))R = mid;
        else L = mid;
    }
}
int main(){
    freopen("Random.in","r",stdin);
    freopen("Random.out","w",stdout);
    scanf("%lld%lld",&n,&m);
    init(n);
    for(LL i = 1;i <= n - 1;i ++){
        scanf("%lld%lld%lld",&a,&b,&c);
        build(a,b,c);
        build(b,a,c);
    }
    dfs(1,1);
    toposort();
    L = R = 0;
    for(LL i = 1;i <= m;i ++){
        scanf("%lld%lld",&e[i].f,&e[i].t);
        LL lca = LCA(e[i].f,e[i].t);
        e[i].v = rank[e[i].f] + rank[e[i].t] - 2*rank[lca];
        e[i].lca = lca;
        R = max(R,e[i].v);
    }
    solve();
    printf("%lld",R);
    fclose(stdin);
    fclose(stdout);
    return 0;
}