#include <iostream>
#include <iomanip>
using namespace std;

int main(){
    double a,b;
    cin >> a >> b;
    cout << fixed << setprecision(10);
    double p = 3.14159265359;
    cout << p * (b - a) - 1 / 3.0 * p * (b * b * b - a * a * a) << endl;
    
}