#include <bits/stdc++.h>
using namespace std;
#define ll long long
int N, R, Q, root;
vector<vector<int>> graph;
vector<map<int, int>> M;
vector<vector<int>> occ;
vector<int> region;
void precompute(int curr){
vector<int> adj = graph[curr];
M[curr][region[curr]]++;
for(int a : adj){
precompute(a);
// bisogna fondere vector[a] in vector[curr]
for(auto m : M[a])
M[curr][m.first]+=m.second;
}
}
void solve(){
cin>>N>>R>>Q>>root;
graph.assign(N+1, vector<int>());
region.assign(N+1, 0);
occ.assign(R+1, vector<int>());
M.assign(N+1, map<int, int>());
region[root] = root;
occ[root].push_back(root);
for(int i = 0; i < N-1; i++){
int a, b;
cin>>a>>b;
graph[a].push_back(i+2);
occ[b].push_back(i+2);
region[i+2] = b;
}
precompute(root);
int ans = 0;
for(int i = 0; i < Q; i++){
int r1, r2;
cin>>r1>>r2;
ans = 0;
vector<int> o = occ[r1];
for(int e : o) ans += M[e][r2];
cout<<ans<<endl;
}
}
int main(){
solve();
return 0;
}
