#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int x,k,y,n,c;
    cout << "tavolsaga1 km, tavolsag2, csuprok szama1, csuprok szma2" << endl;
    cin>>y>>x;
    cin>>k>>n;
    if (k>=y)
    {
        c=k+n-y;
    }
    else
    {
        c=k+n-k;
    }
    cout <<c-abs(x-y)<<endl;
    return 0;
}