#include<cstdio>
using namespace std;
long long f[25][25];
bool g[25][25];
void horse(int x,int y){
    	g[x - 2][y - 1] = 1;
	g[x + 2][y - 1] = 1;
	g[x - 2][y + 1] = 1;
	g[x + 2][y + 1] = 1;
	 g[x - 1][y - 2] = 1;
	 g[x - 1][y + 2] = 1;
	 g[x + 1][y - 2] = 1;
	 g[x + 1][y + 2] = 1;
}

int main() {
	int x1, y1, x2, y2; 
	scanf("%d %d", &x1, &y1);
	scanf("%d %d", &x2, &y2);
	g[x2+2][y2+2] = 1;
        horse(x2+2,y2+2);
       f[2][2]=1;
	for(int i = 2; i <= x1+2; ++i) 
		for(int j = 2; j <= y1+2; ++j) 
			if(!g[i][j]) { 
				if(f[i][j]==0){
					f[i][j]=f[i-1][j]+f[i][j-1];
                           }
				
			} 
	
	printf("%lld\n", f[x1+2][y1+2]);
	return 0;
}

洛谷AC，marsoj90分