import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Back_23971 {
    public static void main(String[] args) throws IOException {

        // given
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine(), " ");
        int H = Integer.parseInt(st.nextToken());
        int W = Integer.parseInt(st.nextToken());
        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());
        int count = 0;

        // when
        for (int i = 1; i <= H; i = i + N + 1) {
            for (int j = 1; j <= W; j = j + M + 1){
                count ++;
            }
        }

        // then
        System.out.println(count);
        br.close();
    }
}