#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    ofstream fout("paint.out");
    ifstream fin("paint.in");
    int a, b, c, d, output, temp;
    fin >> a >> b >> c >> d;

    if (c < a)
    {
        printf("Hello");
        temp = c;
        c = a;
        a = temp;

        temp = b;
        b = d;
        d = temp;
    }

    if (c <= b)
    {
        if (d > b)
        {
            output = d - a;
        }
        else
        {
            output = b - a;
        }
    }

    else
    {
        output = (b - a) + (d - c);
    }

    fout << output << endl;
    return 0;
}