#include <iostream>

int main(void)
{
	int C, in, out;
	scanf("%f", &C);
	scanf("%f", &in);
	scanf("%f", &out);
	
	printf("%f\n", C * 2 * 3.14159 * (in + out) / 2 * 3.14159 * ((in + out) / 2 - in) * ((in + out) / 2 - in));

	return 0;
}