function Main(input) {

    s = input.split("");

    for (var i = 0; i < s.length; i++) {
        s[i] = parseInt(s[i], 10);
    }

    var count0 = 0;
    var count1 = 0;

    for (var i = 0; i < s.length; i++) {
        if (s[i] == 0) {
            count0++;
        }
    }

    for (var i = 0; i < s.length; i++) {
        if (s[i] == 1) {
            count1++;
        }
    }

    var value = Math.min(count0, count1);

    console.log(value * 2);
}



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