import Foundation

func readInt() -> Int {
    return Int(readLine()!)!
}

func readString() -> String {
    return readLine()!
}

func readLines(times: Int) -> [String] {
    var array = [String]()
    for _ in 0..<times {
        array.append(readLine()!)
    }
    return array
}

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

func readStringToStrings() -> [String] {
    return readLine()!.map{String($0)}
}

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

// 二進数に変換
func convertIntToRadix2(n: Int, radix: Int = 2) -> String {
    return String(n, radix: radix)
}

//配列を逆順にする reverced ソートする　sorted
//最初数文字取得 prefix

let abcd = readSeparatedInts()

var products = [Int]()
products.append(abcd[0] * abcd[2])
products.append(abcd[0] * abcd[3])
products.append(abcd[1] * abcd[2])
products.append(abcd[1] * abcd[3])
products.sort { a, b in a > b }
print(products.first!)
