#include <cstdio>
#include <cmath>
double r1, r2, r, ans;
int main() {
	scanf("%lf%lf", &r1, &r2);
	r = r1 < r2 ? r1 : r2;
	double delta = (double) r / 50000000;
	for(double base = delta; base <= r; base += delta) {
		ans += sqrt(r1 * r1 - base * base) * sqrt(r2 * r2 - base * base);
	}
	printf("%.8lf\n", ans * 8 * delta + r1 * r2 * delta * 4);
	return 0;
}