function Main(input) {
    const src = input.replace("\n", "").split(" ");
    const a = parseInt(src[0]);
    const b = parseInt(src[1]);
    const c = parseInt(src[2]);

    const arr = [0, 1, 2, 3];
    let ans = -1;

    if (a == b && a == c && b == c) ans = a;
    if (a != b && a != c && b == c) ans = a;
    if (a != b && a == c && b != c) ans = b;
    if (a == b && a != c && b != c) ans = c;
    if (a != b && a != c && b != c)
        ans = arr.filter(n => n != a && n != b && n != c)[0];

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