import std.stdio, std.conv, std.math, std.string, std.range, std.array,
       std.algorithm;

void main(){
  immutable C = readln().strip().to!int();
  auto buf = readln().strip().split().map!(to!int)();
  immutable I = buf[0];
  immutable O = buf[1];

  writefln("%.10f", C * ((I.to!double-O) ^^ 2 * PI_2 * PI * (O.to!double+I)/2) );
}