#include<bits/stdc++.h>
using namespace std;
const int N = 500001;
int cnt,fa[N][22],n,m,s,head[N],depth[N];
struct qedge{
	int to,next;
}edge[N*2];
void addedge(int x,int y){
	edge[++cnt].to = y;
	edge[cnt].next = head[x];
	head[x] = cnt;
}
void dfs(int now,int fath){
	fa[now][0] = fath,depth[now] = depth[fath] + 1;
	for(int i = 1;i <= log2(depth[now]);i++){
		fa[now][i] = fa[fa[now][i - 1]][i - 1];
	}
	for(int i = head[now];i;i = edge[i].next){
		if(edge[i].to != fath){
			dfs(edge[i].to,now);
		}
	}
}
int LCA(int x,int y){
	if(depth[x] < depth[y]){
		swap(x,y);
	} 
	while(depth[x] > depth[y]){
		x = fa[x][int(log2(depth[x] - depth[y]) - 1)];
	}
	if(x == y)return x;
	for(int k = log2(depth[x]) - 1;k >= 0;k--){
		if(fa[x][k] != fa[y][k]){
			x = fa[x][k],y = fa[y][k];
		}
	}
	return fa[x][0];
}
int main(){
	cin>>n>>m>>s;
	for(int i = 1;i < n;i++){
		int a,b;
		cin>>a>>b;
		addedge(a,b);
		addedge(b,a);
	}
	dfs(s,0);
	for(int i = 1;i <= m;i++){
		int a,b;
		cin>>a>>b;
		cout<<LCA(a,b)<<endl;
	}
} 

我都改的快和题解一样，就是不对？！