"use strict";
    
const main = arg => {
    arg = arg.trim().split("\n");
    const a = BigInt(arg[0].split(" ")[0]);
    const b = BigInt(arg[0].split(" ")[1]);
    const c = BigInt(arg[0].split(" ")[2]);
    const d = BigInt(arg[0].split(" ")[3]);
    
    let answers = [];
    
    answers.push(a * c);
    answers.push(a * d);
    answers.push(b * c);
    answers.push(b * d);
  
    let answer = answers[0];
  
    for(let i in answers) {
      if(answers[i] > answer) {
        answer = answers[i];
      }
    }
    
    console.log(answer.toString());
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));
