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

int n,m,p,q;
int fa[2][10005];//0 man 1 woman

void init(){
    for(int i = 1 ; i <= n ; i++){
        fa[0][i] = i;
    }
    for(int i = 1 ; i <= m ; i++){
        fa[1][i] = i;
    }
}
int find(int flag,int a){
    while(fa[flag][a] != a) a = fa[flag][a];
    return a;
}
void merge(int flag,int a,int b){
    a = find(flag,a);
    b = find(flag,b);
    if(a != b){
        fa[flag][a] = b;
    }
}

int main(){
    int a,b;
    int man = 0,woman = 0;
    cin>>n>>m>>p>>q;
    init();
    for(int i = 1 ; i <= p ; i++){
        cin>>a>>b;
        if(a == b){
            continue;
        }
        merge(0,a,b);
    }
    for(int i = 1 ; i <= q ; i++){
        cin>>a>>b;
        a = 0 - a;
        b = 0 - b;
        if(a == b){
            continue;
        }
        merge(1,a,b);
    }
    for(int i = 1 ; i <= n ; i++){
        if(find(0,i) == find(0,1)){
            man++;
        }
    }
    for(int i = 1 ; i <= m ; i++){
        if(find(1,i) == find(1,1)){
            woman++;
        }
    }
    cout<<min(woman,man)<<endl;
    return 0;
}