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

    rapt(n, m);
}

function rapt(n, m) {
    var day = 0;

    if (n % 2 == 1) {
        day += (m >= n) ? 1 : -1;
    } else if (n % 2 == 0) {
        if (m >= n) {
            day += 1;
        } else {
            day += (m >= (n / 2)) ? 2 : -1;
        }
    }

    console.log(day);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));