function Main(input) {
  input = input.split(" ");
  const a = input[0];
  const b = input[1];
  const c = input[2];
  const d = input[3];

  if(b > 0 && d > 0){
    console.log("%d", b*d);
  }else if(b <= 0 && d <= 0){
    console.log("%d", a*c);
  }else if(b < 0 && d > 0){
    console.log("%d", b*c);
  }else if(b > 0 && d < 0){
    console.log("%d", a*d);
  }else{
    console.log("0");
  }
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));