//code by Emissary
#include<bits/stdc++.h>

#define fi first
#define se second
#define vc vector
#define db double
#define ll long long
#define mk make_pair
#define pb push_back
#define PI pair<int,int>
#define ull unsigned long long
#define err cerr << "   -_-   " << endl
#define debug cerr << " ------------------- " << endl

#define input(x) freopen(#x".in","r",stdin)
#define output(x) freopen(#x".out","w",stdout)

#define NO puts("No")
#define YES puts("Yes")

//#define int long long

using namespace std;

namespace IO{
	inline int read(){
		int X=0, W=0; char ch=getchar();
		while(!isdigit(ch)) W|=ch=='-', ch=getchar();
		while(isdigit(ch)) X=(X<<1)+(X<<3)+(ch^48), ch=getchar();
		return W?-X:X;
	}
	inline void write(ll x){
		if(x<0) x=-x, putchar('-');
		if(x>9) write(x/10);
		putchar(x%10+'0');
	}
	inline void sprint(ll x){write(x), putchar(32);}
	inline void eprint(ll x){write(x), putchar(10);}
}using namespace IO;

const int MAXN = 3e5+5;

int n, m, sum[MAXN], type[MAXN];
int ta[MAXN], tb[MAXN], siz[MAXN], tp[MAXN], bel[MAXN];
int head[MAXN], ne[MAXN<<1], to[MAXN<<1], de[MAXN], cnt;

set<PI> num1[MAXN], num2[MAXN];

ll minans;

vc<PI> ans;

inline void add(int x, int y){++cnt;to[cnt]=y;ne[cnt]=head[x];head[x]=cnt;}

inline void dfs(int x, int f){
	siz[x]=(ta[x]?1:0)-(tb[x]?1:0); sum[x]=(ta[x]?1:0)+(tb[x]?1:0); de[x]=de[f]+1;
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		dfs(to[i],x); siz[x]+=siz[to[i]]; sum[x]+=sum[to[i]];
		if(!sum[to[i]]) continue;
		minans+=max(2,abs(siz[to[i]])*2);
	}
	return ;
}

inline void construct(int x, int f){
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		if(siz[to[i]]>=0) construct(to[i],x);
		else continue;
		if(num1[x].size()<num1[to[i]].size()) swap(num1[x],num1[to[i]]);
		for(auto j:num1[to[i]]) num1[x].insert(j);
	}
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		if(siz[to[i]]<0) construct(to[i],x);
		else continue;
		if(num2[x].size()<num2[to[i]].size()) swap(num2[x],num2[to[i]]);
		for(auto j:num2[to[i]]) num2[x].insert(j);
	}
	if(ta[x]) num1[x].insert(mk(de[x],ta[x])), bel[ta[x]]=ans.size(), ans.pb(mk(ta[x],0));
	if(tb[x]) num2[x].insert(mk(de[x],tb[x]));
	while(num1[x].size() && num2[x].size()){
		int s, t;
		s=(*num1[x].rbegin()).se;
		t=(*num2[x].rbegin()).se;
		ans[bel[s]].se=t;
		num1[x].erase(*num1[x].rbegin());
		num2[x].erase(*num2[x].rbegin());
	}
	return ;
}

signed main(){
	n=read(), m=read();
	for(int i=1;i<=m;++i) ta[read()]=i;
	for(int i=1;i<=m;++i) tb[read()]=i;
	for(int i=2;i<=n;++i){
		int x, y;
		x=read(), y=read();
		add(x,y), add(y,x);
	}
	dfs(1,0); construct(1,0);
	eprint(minans);
	for(auto i:ans) sprint(i.fi), sprint(i.se);
	return 0;
}