Problem:
Score : 200 points

Problem Statement

Alice and Bob are controlling a robot. They each have one switch that controls the robot.

Alice started holding down her button A second after the start-up of the robot, and released her button B second after the start-up.

Bob started holding down his button C second after the start-up, and released his button D second after the start-up.

For how many seconds both Alice and Bob were holding down their buttons?

Constraints

0≤A<B≤100

0≤C<D≤100

All input values are integers.

Input

Input is given from Standard Input in the following format:

A B C D

Output

Print the length of the duration (in seconds) in which both Alice and Bob were holding down their buttons.

Sample Input 1

0 75 25 100

Sample Output 1

50

Alice started holding down her button 0 second after the start-up of the robot, and released her button 75 second after the start-up.

Bob started holding down his button 25 second after the start-up, and released his button 100 second after the start-up.

Therefore, the time when both of them were holding down their buttons, is the 50 seconds from 25 seconds after the start-up to 75 seconds after the start-up.

Sample Input 2

0 33 66 99

Sample Output 2

0

Alice and Bob were not holding their buttons at the same time, so the answer is zero seconds.

Sample Input 3

10 90 20 80

Sample Output 3

60

Solution in JavaScript (node.js v5.12) (judge verdict: Accepted)

var debug = false;

function check(a,b,c,d){
  if(debug) { console.log("END"); }
  if(a <= c) {
    if(c <= b) {
        // a   c (d)  b  (d)
        return Math.min(b,d) - c;
    } else {
        // a   b   c    d
        return 0;
    }
  } else {
    // c < a
    // c (d) a (d) b (d)
    if( d <= a ) {
      // c d a b
      return 0;
    } else {
      // c a  (d) b (d)
      return Math.min(b,d) - a;
    }

  }
  return -1;
}

function Main(inp) {
  var input = inp.split("\n");
  if(debug) {console.log(input)}
  var tmp = input[0].split(" ");
  if(debug) { console.log(parseInt(tmp[0],10))}
  var target = tmp.map(function(x){return parseInt(x,10);});
  if(debug) {console.log(target)}

  console.log(check(target[0],target[1],target[2],target[3]));
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));