这也能死循环？测了是indepth有问题但是目测并不会死循环。。

#include<bits/stdc++.h>
using namespace std;

const int maxn = 5e5 + 5;
const int maxm = 5e5 + 5;

inline int read() {
	int ret = 0, f = 1;char ch = getchar();
	while (ch < '0' || ch > '9') {
		if (ch == '-') f = -f;
		ch = getchar();
	}
	while (ch >= '0' && ch <= '9') {
		ret = (ret << 1) + (ret << 3) + (ch ^ 48);
		ch = getchar();
	}
	return ret * f;
}

int tot, head[maxn], to[maxm], nxt[maxm];
void add(int u, int v) {
	tot++;
	nxt[tot] = head[u];
	head[u] = tot;
	to[tot] = v;
}

int n, m, s;

int dep[maxn], fa[maxn][31];
void indepth(int now, int root) {
	fa[now][0] = root;
	dep[now] = dep[fa[now][0]] + 1;
	
	for (int i = 1;(1 << i) <= n;i++) {
		fa[now][i] = fa[fa[now][i - 1]][i - 1];
	}
	
	for (int i = head[now];i;i = nxt[i]) {
		int v = to[i];
		if (v == root) continue;
		indepth(v, now);
	}
	return;
}

int LCA(int x, int y) {
	if (dep[x] > dep[y]) swap(x, y);
	
	int ans = 0;
	while (dep[x] < dep[y]) x = fa[x][0], ans++;
	
	for (int i = 1;(1 << i) <= dep[x];i++) {
		if (fa[x][0] == fa[y][0]) break;
		x = fa[x][i];
		y = fa[y][i];
		ans += (1 << i);
	}
	return ans;
}

int main() {
	n = read(), m = read(), s = read();
	for (int i = 1;i <= n;i++) {
		int a = read(), b = read();
		add(a, b), add(b, a);
	}
	
	for (int i = head[s];i;i = nxt[i]) {
		int v = to[i];indepth(v, s);
	}
	
	for (int i = 1;i <= m;i++) {
		int a = read(), b = read();
		int ans = LCA(a, b);
		if (ans == 0) puts("-1");
		else printf("%d\n", ans);
	}
	
	return 0;
}