function gcd(a, b) {
    if (a%b === 0) return b;
    return gcd(b, a%b);
}

function lcm(a, b) {
    return a * b / gcd(a, b)
}

function Main(input) {
    var N = parseInt(input);
    
    console.log(lcm(N, 2));
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));