/*
Concentric Circles

Write a C program that calculates the area of the white surface 
shown in the figure. The program must ask the user to enter the 
radius of the outer circle and also the radius of the inner circle.
The output must be formatted with exactly three significant digits after the decimal point.
 
============= START OF SAMPLE RUN =======================
Enter the outer radius: 2.5
Enter the inner radius: 1.5
 
The area of the white surface is: 12.566
=============  END OF SAMPLE RUN  =======================  
 
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>


int main()
{
	double r1, r2;
	
	printf("Enter the outer radius: ");
	scanf("%lf", &r2);

	printf("Enter the inner radius: ");
	scanf("%lf", &r1);
	
	double area;
	area = M_PI*r2*r2 - M_PI*r1*r1;
	
	printf("\nThe area of the white surface is: %.3f\n", area);
	system("pause");
	return 0;
}