var toInt = x=>parseInt(x,10);
var toIntArr = arr=>arr.map(x=>toInt(x));
var abs = x=>x>0?x:-x;
function min(){var rest = arguments,val=rest[0];for(var i=1;i<rest.length;i++)if(rest[i]<val)val = rest[i];return val}
function max(){var rest = arguments,val=rest[0];for(var i=1;i<rest.length;i++)if(rest[i]>val)val = rest[i];return val}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
 
function Main(input){
	var input = input.split(' ');
	var n = toInt(input[0]);
	var m = toInt(input[1]);
	var d = toInt(input[2]);
	var nmd0 = 0;
	for(var j = 1; j <= n; j++){
		nmd0 += (j+d<=n)? 1:0;
		if(d!==0) nmd0 += (j-d>=1)? 1:0;
	}
	nmd0 /= n*n;
	var ans = nmd0 * (m-1);

	console.log(ans);
}