#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "iomanip"
#include "cmath"

using namespace std;

const long long int MOD = 1000000007;

long long int N, M, K, H, W, L, R;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	long double a, b;
	cin >> a >> b;
	a = max(a, (long double) - 1);
	b = min(b, (long double)1);
	long double ans=0;
	long double box = (b - a) / 10000000;
	long double c = a;
	for(int i=0;i<10000000;i++){
		ans += sqrt((long double)1 - a*a)*3.1415926535 * 2;
		a += box;
	}
	ans /= 10000000;
	ans *= (b - c);
	ans *= 1.273239544;
	cout << setprecision(20) << ans << endl;
	return 0;
}