function Main(input) {
    var line = input.split(" ");
    var L = +line[0];
    var K = +line[1];

    rapt(L, K);
}

function rapt(L, K) {
    var total = 0;
    do {
        L -= (K * 2);

    total += (L > 0) ? K : 0;
        
    } while (L > 0);

    console.log(total);
} 

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