ways[x][y]
#x行y个数
bx=input()
by=input()
hx=input()
hy=input()
ways[0][0]=0
for i in range(1,by+1):
    ways[0][i]=1
for l in range(1,bx+1):
    ways[l][0]=1
ways[hx][hy]=0
for x in range(1,bx+1):
    for y in range(1,by+1):
        ways[x][y]=ways[x-1][y]+ways[x][y-1]
print(ways[bx][by])

#include<bits/stdc++.h>
using namespace std;
long long bx,by,hx,hy;
int main()
{
	long long x,y;
	cin>>bx>>by;
	cin>>hx>>hy;
	x=bx;
	y=by;
	long long ways[x][y];
	ways[0][0]=0;
	for(int i=1;i<=by;++i)
	{
		ways[0][i]=1;
	}
	for(int l=1;l<=bx;++l)
	{
		ways[l][0]=1;
	}
	ways[hx][hy]=0;
	for(long long x=1;x<=bx;++x)
	{
		for(long long y=1;y<=by;++y)
		{
			ways[x][y]=ways[x-1][y]+ways[x][y-1];
		}
	}
	cout<<ways[bx][by];
	return 0;
 } 

RE...