import std.stdio;
import std.string;
import std.conv;
import std.algorithm;
import std.math;

void main(){
  auto C = readln.chomp.to!int;
  auto buf = readln.chomp.split(" ").map!(to!double);
  double Rin = buf[0];
  double Rout = buf[1];
  double r = (Rout - Rin) / 2;
  double donutR = Rin + r;
  double donutVolume = (PI * r^^2) * (2 * PI * donutR);
  writefln("%.10f", donutVolume * C);
}