/*
	yukicoder No.89 どんどんドーナツどーんといこう！
	解答者：ヒロソフ
*/
#define _USE_MATH_DEFINES
#include <stdio.h>
#include <math.h>
double GetDonutVolime(double inRadius, double outRadius);
int main(void) {
	int c,in, out;
	scanf("%d", &c);
	scanf("%d %d", &in , &out);
	printf("%.10f\n", c * GetDonutVolime(in, out));
	return 0;
}
double GetDonutVolime(double inRadius, double outRadius) {
	return 0.25 * M_PI * M_PI * (inRadius + outRadius) * (outRadius - inRadius)* (outRadius - inRadius);
}