// URL: https://yukicoder.me/problems/no/724

import std.algorithm, std.array, std.container, std.math, std.range, std.typecons, std.string;

version(unittest) {} else
void main()
{
  int n; double a, b; io.getV(n, a, b);

  auto c = (a+b)/2, d = (a*b).sqrt, eps = 1.0e-12L;

  struct Cir
  {
    real x, y, r;
    this(double x)
    {
      this.x = x;
      y = (d^^2 * (1 - (x-c)^^2/c^^2)).sqrt;
      r = ((x-a)^^2 + y^^2).sqrt - a;
    }
  }

  Cir e;
  if (n%2 == 1) {
    e = Cir(a+b);
    n = (n-1)/2;
  } else {
    auto calc1(double x)
    {
      auto e = Cir(x);
      return e.r - e.y;
    }
    auto bs = iota(0.0, a+b, eps).map!(x => tuple(x, calc1(x))).assumeSorted!"a[1]<b[1]";
    auto x = bs.lowerBound(tuple(0, 0)).back[0];
    e = Cir(x);
    n = n/2-1;
  }

  auto calc(Cir e, double x2)
  {
    auto e2 = Cir(x2);
    return (e2.r+e.r) - ((e2.x-e.x)^^2+(e2.y-e.y)^^2).sqrt;
  }

  foreach (_; 0..n) {
    auto bs = iota(0.0, e.x, eps).map!(x2 => tuple(x2, calc(e, x2))).assumeSorted!"a[1]<b[1]";
    auto x2 = bs.lowerBound(tuple(0, 0)).back[0];
    e = Cir(x2);
  }

  io.put(e.r);
}

auto io = IO!()();
import std.stdio;
struct IO(string floatFormat = "%.10f", string delimiter = " ", alias IN = stdin, alias OUT = stdout)
{
  import std.conv, std.format, std.meta, std.traits;

  auto getV(T...)(ref T v) { foreach (ref w; v) get(w); }
  auto getA(T)(size_t n, ref T v) if (hasAssignableElements!T)
  { v = new T(n); foreach (ref w; v) get(w); }
  auto getC(T...)(size_t n, ref T v)
  if (allSatisfy!(hasAssignableElements, T))
  {
    foreach (ref w; v) w = new typeof(w)(n);
    foreach (i; 0..n) foreach (ref w; v) get(w[i]);
  }
  auto getM(T)(size_t r, size_t c, ref T v)
  if (hasAssignableElements!T && hasAssignableElements!(ElementType!T))
  {
    v = new T(r); foreach (ref w; v) getA(c, w);
  }
  template getS(E...)
  {
    auto getS(T)(size_t n, ref T v)
    {
      v = new T(n); foreach (ref w; v) foreach (e; E) mixin("get(w."~e~");");
    }
  }

  auto put(bool flush = false, T...)(T v)
  {
    foreach (i, w; v) { putA(w); if (i < v.length-1) OUT.write(delimiter); }
    OUT.writeln;
    static if (flush) OUT.flush();
  }
  auto putB(S, T)(bool c, S t, T f) { if (c) put(t); else put(f); }
  auto putRaw(T...)(T v) { OUT.write(v); OUT.writeln; }

  private
  {
    dchar[] buf;
    auto sp = (new dchar[](0)).splitter;
    void nextLine() { IN.readln(buf); sp = buf.splitter; }
    auto get(T)(ref T v) { if (sp.empty) nextLine(); v = sp.front.to!T; sp.popFront(); }

    auto putR(T)(T v)
    {
      auto w = v;
      while (!w.empty) { putA(w.front); w.popFront(); if (!w.empty) OUT.write(delimiter); }
    }
    auto putA(T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putR(v);
      else if (isFloatingPoint!T) OUT.write(format(floatFormat, v));
      else OUT.write(v);
    }
  }
}