import std;

int calc(int a, int b) {
    if (b == 0) return 1;
    if (a == -1) return 2;
    return -1;
}

void main() {
    int a, b; scan(a, b);
    writeln(calc(a, b));
}

void scan(T...)(ref T a) {
    string[] ss = readln.split;
    foreach (i, t; T) a[i] = ss[i].to!t;
}
T read(T=string)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readints = reads!int;