s=input().split()
s[0]=int(s[0])
s[1]=int(s[1])
s[2]=int(s[2])
s[3]=int(s[3])
a={}
for i in range(0,s[0]+1):
    for j in range(0,s[0]+1):
        a[(i,j)]=0
for i in range(0,s[0]+1):
    a[(i,0)]=1
    a[(0,i)]=1
for i in range(1,s[0]+1):
    for j in range(1,s[1]+1):
        a[(i,j)]=a[(i-1,j)]+a[(i,j-1)]
        if (i,j)==(s[2],s[3]) or (i,j)==(s[2]+1,s[3]+2) or (i,j)==(s[2]+2,s[3]+1) or (i,j)==(s[2]+2,s[3]-1) or (i,j)==(s[2]+1,s[3]-1) or (i,j)==(s[2]-1,s[3]+2) or (i,j)==(s[2]-2,s[3]+1) or (i,j)==(s[2]-2,s[3]-1) or (i,j)==(s[2]-1,s[3]-1):
            a[(i,j)]=0
print(a[(s[0],s[1])])