"use strict";

const is_palindrome = s => {
    let n = s.length;
    for (let i = 0; i < n; i++) {
        if (s[i] !== s[n - i - 1]) return false;
    }

    return true;
}

const main = (input) => {
    const spi = input.split('\n');
    const n = Number(spi[0]);
    const d = n / 3;
    console.log(d*d*d);
};

main(require("fs").readFileSync("/dev/stdin", "utf8"));
