import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}

void main()
{
  int n, m, d; readV(n, m, d);

  if (d == 0)
    writefln("%.7f", 1.0L/n*(m-1));
  else
    writefln("%.7f", 2.0L*(n-d)/n/n*(m-1));
}
