func padLeft(_ instr: String, _ len:Int)-> String {
    var tmp = ""
    for _ in instr.count...len {
        tmp += "0"
    }
    return tmp + instr
}

let person1 = readLine()!.split(separator: " ").map(String.init)
let person2 = readLine()!.split(separator: " ").map(String.init)

let mojilen = max(person1[1].count, person2[1].count)
let yuru1 = padLeft(person1[1], mojilen)
let yuru2 = padLeft(person2[1], mojilen)

if(yuru1 == yuru2) {
    print(-1)
} else if(yuru1>yuru2) {
    print(person1[0])
} else {
    print(person2[0])
}