'use strict';

const main = arg => {
  const [a, b, c, d] = arg.trim().split(' ').map(x => BigInt(x));
  if (a*c > 0) var ans = (a*c > b*d ? a*c : b*d);
  if (a*c == 0) var ans = (a == 0 ? b*d : a*c);
  if (a*c < 0) var ans = (a*d > b*d ? a*d : b*d);
  console.log(ans.toString());
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));