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

using namespace std;

const double pi = acos(-1);

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

  double ans = 0;
  const int N = 1e6;
  double dx = (b - a) / N;
  for (int i = 0; i < N; i++) {
    double x1 = a + i*dx;
    double x2 = a + (i+1)*dx;
    double y1 = sqrt(1-x1*x1);
    double y2 = sqrt(1-x2*x2);
    ans += pi * (y1+y2) * sqrt(dx*dx+(y2-y1)*(y2-y1));
  }

  printf("%.20f\n", (double)ans);
}