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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int INF = (int) 1e9 + 123;
const ll LINF = (ll) 1e18 + 123;
const ld EPS = (ld) 1e-12;
const ll MOD = (ll) 1e9 + 7;

#define sz(x) (int) (x).size()
#define mp(x, y) make_pair(x, y)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define lb(s, t, x) (int) (lower_bound(s, t, x) - s)
#define ub(s, t, x) (int) (upper_bound(s, t, x) - s)
#define rep(i, f, t) for (auto i = f; i < t; i++)
#define per(i, f, t) for (auto i = f; i >= t; i--)

ll power(ll x, ll y, ll mod = MOD) {
    if (y == 0) {
        return 1;
    }
    if (y & 1) {
        return power(x, y - 1, mod) * x % mod;
    } else {
        ll tmp = power(x, y / 2, mod);
        return tmp * tmp % mod;
    }
}

void add(ll &x, ll y, ll mod = MOD) {
    x += y;
    if (x >= mod) x -= mod;
    if (x < 0) x += mod;
}

ll sum(ll x, ll y, ll mod = MOD) {
    add(x, y, mod);
    return x;
}

ll mult(ll x, ll y, ll mod = MOD) {
    return (x * y) % mod;
}

ll div(ll x, ll y, ll mod) {
    return x * power(y, mod - 2, mod);
}

template<typename A, typename B> bool mini(A &x, const B &y) {
    if (y < x) {
        x = y;
        return true;
    }
    return false;
}

template<typename A, typename B> bool maxi(A &x, const B &y) {
    if (y > x) {
        x = y;
        return true;
    }
    return false;
}

template<typename T> void read(T first, T last) {
    while (first != last) {
        cin >> *(first++);
    }
}

template<typename T> void print(T first, T last) {
    while (first != last) {
        cout << *(first++) << " ";
    }
    cout << "\n";
}

void run();

#define TASK ""

int main() {
#ifdef LOCAL
    if (strlen(TASK) > 0) {
        cerr << "Reminder: you are using file i/o, filename: " TASK "!" << endl << endl;
    }
#endif
#ifndef LOCAL
    if (strlen(TASK)) {
        freopen(TASK ".in", "r", stdin);
        freopen(TASK ".out", "w", stdout);
    }
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
#endif
    cout << fixed << setprecision(12);
    run();
    return 0;
}

// == SOLUTION == //

void run() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int l = max(a, c);
    int r = min(b, d);
    cout << max(0, r - l) << "\n";
}