process.stdin.resume();
process.stdin.setEncoding('utf8');
var lines = [];
var max;
var t = [];
var reader = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});
reader.on('line', (line) => {
  lines.push(line);
});
reader.on('close', () => {
  var x = lines[0].split(' ');
  var a = parseInt(x[0]);
  var b= parseInt(x[1]);
  var c = parseInt(x[2]);
  var d = parseInt(x[3]);
  t.push(a*c);
  t.push(a*d);
  t.push(b*c);
  t.push(b*d);
  max = Math.max.apply(null,t);
  if(max == 0){
    max = Math.abs(max);
  }
  console.log(max);
});