#include <bits/stdc++.h>
using namespace std;
int point_x, point_y, horse_x, horse_y;
struct mtype
{
    int num;
    bool have_visted = false;
} memory[1001][1001];
inline bool memcheck(int x, int y, int &num, bool save_or_read)
{
    if (save_or_read)
    {
        memory[x][y].num = num;
        memory[x][y].have_visted = true;
        return true;
    }
    else
    {
        if (memory[x][y].have_visted)
        {
            num = memory[x][y].num;
            return true;
        }
        else
            return false;
    }
}
inline bool check(int x, int y)
{
    if (x == horse_x and y == horse_y)
        return false;
    if (x == horse_x - 2)
    {
        if (y == horse_y - 1)
            return false;
        else if (y == horse_y + 1)
            return false;
    }
    if (x == horse_x + 2)
    {
        if (y == horse_y - 1)
            return false;
        else if (y == horse_y + 1)
            return false;
    }
    if (x == horse_x - 1)
    {
        if (y == horse_y - 2)
            return false;
        else if (y == horse_y + 2)
            return false;
    }
    if (x == horse_x + 1)
    {
        if (y == horse_y - 2)
            return false;
        else if (y == horse_y + 2)
            return false;
    }
    return true;
}
int run(int x, int y)
{
    int ret=0;
    if(x==0 or y==0)
        return 1;
    if(memcheck(x,y,ret,false))
        return ret;
    if(!check(x,y))
        return 0;
    ret=run(x - 1, y) + run(y - 1, x);
    memcheck(x,y,ret,true);
    return ret;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cin >> point_x >> point_y >> horse_x >> horse_y;
    cout << run(point_x, point_y) << endl;
    return 0;
}

谢谢大佬！