const main = stdin => {
    const input = stdin.trim().split('\n')
    //ここにかく
    //文字列S
const a = parseInt(input[0].split(" ")[0]),
      b = parseInt(input[0].split(" ")[1]),
      c = parseInt(input[0].split(" ")[2]),
      d = parseInt(input[0].split(" ")[3]);

const E = a*c;
const D = a*d;
const F = b*c;
const G = b*d;

console.log(Math.max(E, D, F, G));
    
};
    // 標準入力
    main(require("fs").readFileSync("/dev/stdin", "utf8"))