#80分MLE求调

#include <bits/stdc++.h>
#define N 10000
using namespace std;
long long a[N][N] , n , m , s1 , s2 , q , w , ss;
int main(){	
    cin >> n >> m >> s1 >> s2;
    while(s1--&&cin >> q >> w){
    	for(int i = q;i <= w;i++){
    		for(int j = 1;j <= m;j++){
    			if(a[i][j] != 1){
    				a[i][j] = 1;
    				ss++;
				}
			}
		}
	}
	while(s2--&&cin >> q >> w){
    	for(int i = q;i <= w;i++){
    		for(int j = 1;j <= n;j++){
    			if(a[j][i] != 1){
    				a[j][i] = 1;
    				ss++;
				}
			}
		}
	}
	cout << ss;
	return 0;
}