钉子精神就是钻牛角尖的精神（逃

#include<bits/stdc++.h>
using namespace std;
#define debug(x) cerr<<#x<<' '<<x<<endl
template<class T>void read(T&x){
	short f=1;x=0;
	char ch=getchar();
	while(!isdigit(ch)){
		if(ch=='-')f=-1;
		ch=getchar();
	}while(isdigit(ch)){
		x=(x<<1)+(x<<3)+(ch^48);
		ch=getchar();
	}x*=f;
}
template<class T>void write(T x){
	if(x<0)putchar('-'),x=-x;
	if(x>10)write(x/10);
	putchar(x%10+48);
}
#define maxn 150010
int n,m,x,y;
int head[maxn],Next[maxn<<1],ver[maxn<<1],tot;
void add(int x,int y){
	ver[++tot]=y;
	Next[tot]=head[x];
	head[x]=tot;
}
int top[maxn],fa[maxn],dep[maxn],son[maxn],siz[maxn],cnt,dfn[maxn];
void dfs1(int x){
	siz[x]=1;
	for(int i=head[x];i;i=Next[i]){
		int y=ver[i];
		if(dep[y])continue;
		dep[y]=dep[x]+1;
		fa[y]=x;
		dfs1(y);
		siz[x]+=siz[y];
		if(siz[son[x]]<siz[y])son[x]=y;
	}
}
void dfs2(int x,int y){
	top[x]=y;
	dfn[x]=++cnt;
	if(siz[x]==0)return;
	dfs2(son[x],y);
	for(int i=head[x];i;i=Next[i])
	if(ver[i]!=fa[x]&&ver[i]!=son[x])dfs2(ver[i],ver[i]);
}
struct{
	int c[maxn];
	inline int ask(int x){
		int ans=0;
		for(;x;x-=x&-x)ans+=c[x];
		return ans;
	} 
	inline void add(int x,int y){
		for(;x<=n;x+=x&-x)c[x]+=y;
	}
	inline void add(int x,int y,int z){
		add(x,z),add(y+1,-z);
	}
}s; 
void change(int x,int y){
	while(top[x]!=top[y]){
		if(dep[top[x]]<dep[top[y]])swap(x,y);
	//	cout<<"From "<<top[x]<<" to "<<x<<endl;
		s.add(dfn[top[x]],dfn[x],1),x=fa[top[x]];
	}
	if(dep[x]>dep[y])swap(x,y);
	s.add(dfn[x],dfn[y],1);
}
signed main(){
#ifndef ONLINE_JUDGE
	freopen("testdata.in","r",stdin);
#endif
	read(n),read(m);
	for(int i=1;i<n;i++){
		read(x),read(y);
		add(x,y),add(y,x);
	}
	dep[1]=1;
	dfs1(1);
	dfs2(1,1);
	while(m--){
		read(x),read(y);
		change(x,y);
	}
	int ans=0;
	for(int i=1;i<=n;i++)ans=max(ans,s.ask(dfn[i]));
	write(ans);
}

$maxn$开$50010$就过不了，我明明存边的时候乘$2$了鸭，好奇怪