import std.algorithm;
import std.array;
import std.conv;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

real solve (int n, int m, int d)
{
	if (d == 0)
	{
		return 1.0L / n * (m - 1);
	}
	return 2.0L * (n - d) / n / n * (m - 1);
}

void main ()
{
	int n, m, d;
	while (readf (" %s %s %s", &n, &m, &d) > 0)
	{
		writefln ("%.10f", solve (n, m, d));
	}
}
