function Main(input) {
	var str = input;
	var ans = 0;
	str = str.split("\n");
	var l = Number(str[0].split(" ")[0]); 	
 	var n = (l / 3).toFixed(6);
 	var ans = (n**3).toFixed(6);
 	console.log(ans);
}
 //*おまじない
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
