#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 = sqrt((long double)1 - a*a)*a + asin(a);
	b = sqrt((long double)1 - b*b)*b + asin(b);
	cout << setprecision(20) << (b - a) * 4 << endl;
	return 0;
}