树剖模板炸了

#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
int n, m, s, dep[N], siz[N], fa[N], son[N], top[N];
vector <int> p[N];
void dfs1(int u) {
	siz[u] = 1;
	for (auto to : p[u]) {
		if (to == fa[u]) continue ;
		fa[to] = u;
		dep[to] = dep[u] + 1;
		dfs1(to);
		siz[u] += siz[to];
		if (siz[son[u]] < siz[to]) son[u] = to;
	}
}
void dfs2(int u) {
	for (auto to : p[u]) {
		if (to == fa[u]) continue ;
		top[to] = (son[u] == to) ? top[u] : to;
		dfs2(to);
	}
}
void read(int &x) {
	x = 0;
	char c = getchar();
	while (!isdigit(c)) c = getchar();
	while (isdigit(c)) x = x * 10 + c - '0', c = getchar();
}
int main() {
	read(n), read(m), read(s);
	for (int i = 1, u, v; i < n; ++i) {
		read(u), read(v);
		p[u].push_back(v);
		p[v].push_back(u);
	}
	dfs1(s);
	top[s] = s, fa[s] = s;
	dfs2(s);
	while (m--) {
		int x, y;
		read(x), read(y);
		while (top[x] != top[y])
			(dep[x] > dep[y]) ? x = fa[top[x]] : y = fa[top[y]];
		printf("%d\n", (dep[x] < dep[y]) ? x : y);
	}
	return 0;
}