#include<iostream>

int main(void)
{
    int C, in, out;
	scanf("%d", &C);
	scanf("%d", &in);
	scanf("%d", &out);
	
	printf("%f\n", C * 2 * 3.14 * (in + out) / 2 * 3.14 * ((in + out) / 2 - in) * ((in + out) / 2 - in));
    return 0;
}