import java.util.*;

public class Main{
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int a = scan.nextInt();
		int b = scan.nextInt();
		int h = scan.nextInt();
		int m = scan.nextInt();
		scan.close();
		
		double rad = Math.PI * 2 * ((double)h / 12.0 + ((double)m / 60.0) / 12.0 - (double)m / 60.0);
		double rsq = (double)(a * a + b * b) - (double)(2 * a * b) * Math.cos(rad);
		 
		System.out.println(Math.sqrt(rsq));
	}
}