#include <bits/stdc++.h>
using namespace std;

int bs = 0;

void bz(int x,int y,int bx,int by,int mx,int my)

{
    if ((!((mx==x)&(my==y))) & ((x <= bx) & (y <= by)) & ((! ((x==mx-1) & (y==my-2)))) & ((! ((x==mx-2) & (y==my-1)))) & ((! ((x==mx+1) & (y==my+2)))) & ((! ((x==mx+2) & (y==my+1)))) & ((! ((x==mx-1) & (y==my+2)))) & ((! ((x==mx-2) & (y==my+1)))) & ((! (((x==mx+1) & (y==my-2))))) & ((! (((x==mx+2) & (y==my-1))))))
    {
        bz (x+1,y,bx,by,mx,my);
        bz (x,y+1,bx,by,mx,my);
        if ((x == bx) & (y == by))
        {
            bs += 1;
        }
    }
}

int main()
{
    int mxx , myy , bxx , byy;
    cin >> bxx >> byy >> mxx >> myy ;
    bz(0,0,bxx,byy,mxx,myy);
    cout << bs;
    return 0;
}

四十分，谁能帮帮我