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

int record[22][22];
int bx,by,cx,cy;

int path(int x,int y){
    if(x==0 || y==0)return 0;
    if((x-cx)*(x-cx)+(y-cy)*(y-cy) == 5 || (x==cx && y==cy))return 0;
    if(record[x][y] == 0)record[x][y] = path(x-1,y)+path(x,y-1);
    return record[x][y];
}

int main(){
    record[1][1]=1;
    cin >> bx >> by >> cx >> cy;
    cx++;cy++;
    cout << path(bx+1,by+1);
}