RT.

#include <iostream>
#include <cstdio>
#pragma GCC optmize(2)
using namespace std;
struct edge
{
    int u, v, nxt;
} a[1000010];
int f[500010][23], dep[500010], edgegs, head[500010];
int addln(int u, int v)
{
    a[++edgegs].u = u;
    a[edgegs].v = v;
    a[edgegs].nxt = head[u];
    head[u] = edgegs;
}
int log_2[1000010];
int rc(int fa, int now)
{
    f[now][0] = fa;
    dep[now] = dep[fa] + 1;
    for (int i = 1; i <= log_2[dep[now]]; i++)
        f[now][i] = f[f[now][i - 1]][i - 1];
    for (int i = head[now]; i; i = a[i].nxt)
        if (a[i].v != fa)
            rc(now, a[i].v);
}
int lca(int l, int r)
{
    if (dep[r] < dep[l])
        swap(l, r);
    while (dep[r] > dep[l])
        r = f[r][log_2[dep[r] - dep[l]] - 1];
    if (l == r)
        return l;
    for (int i = log_2[dep[l]] - 1; i >= 0; i--)
    {
        if (f[l][i] != f[r][i])
        {
            l = f[l][i];
            r = f[r][i];
        }
    }
    return f[r][0];
}
int main()
{
    int n, m, s;
    scanf("%d%d%d", &n, &m, &s);
    int u, v;
    for (int i = 1; i < n; i++)
        log_2[i] = log_2[i - 1] + (1 << log_2[i - 1] == i);
    for (int i = 1; i < n; i++)
    {
        scanf("%d%d", &u, &v);
        addln(u, v);
        addln(v, u);
    }
    rc(0, s);
    for (int i = 0; i < m; i++)
    {
        scanf("%d%d", &u, &v);
        printf("%d\n", lca(u, v));
    }
    return 0;
}