#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>

using namespace std;

const double pi = acos(-1);

double f(double x) {
  return pi * (1 - x*x);
}

int main() {
  double a, b;
  cin >> a >> b;

  double ans = (f(a) + 4*f((a + b) / 2) + f(b)) * (b - a) / 2;
  printf("%.20f\n", ans);
}