func readInts() -> [Int] {
    return readLine()!.split(separator: " ").map { Int($0)! }
}

func main1() {
    let param = readInts()
    
    var ans = param[1] * param[3]
    
    for i in 0...1 {
        for j in 2...3 {
            if (param[i] * param[j] > ans){
                ans = param[i] * param[j]
            }
        }
    }
    
    print(ans)
}

main1()