import java.util.*;
 
public class Main {
	public static void main(String[] args) {
	Scanner sc  = new Scanner(System.in);
    double ans = 0;
    int C   = Integer.parseInt(sc.next());
    int a   = Integer.parseInt(sc.next());
    int b   = Integer.parseInt(sc.next());
    ans = C*(b*b-a*a)*(b-a)*2.46740110027;
    System.out.print(ans);
    System.out.println();
	}
        
}