import std.stdio, std.conv, std.string, std.bigint;
import std.math, std.random, std.datetime;
import std.array, std.range, std.algorithm, std.container;
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }

void main(){
	real n = read.to!real;
	real m = read.to!real;
	real d = read.to!real;
	
	real ans;
	if(d == 0.0) ans = (m - 1.0) / n;
	else ans = (m - 1.0) * 2 * (n - d) / n / n;
	
	ans.writeln;
	}
	
	