"use strict"
function main(arg) {
    let [a,b,c,d] = arg.trim().split("\n")[0].split(" ").map(Number)
    // a = 10e9
    // c = 10e9
    let max = Math.max(
        a*c,
        a*d,
        b*c,
        b*d,
    )
    console.log(max)
    // console.log([a,b,c,d])
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));