Bx,By,Mx,My=list(map(int,input().split()))
Bx+=2
By+=2
Mx+=2
My+=2
dp=[]
for i in range(40):
    dp.append([0]*(40))
ss=[]
for i in range(40):
    ss.append([0]*40)    
ss[Mx][My]=1
Mxl=[0,-2,-1, 1, 2, 2, 1,-1,-2]
Myl=[0, 1, 2, 2, 1,-1,-2,-2, 1]
dp[2][1]=1  
for i in range(9):           
    ss[Mx+Mxl[i]][My+Myl[i]]=1
for i in range(2,Bx+1):
    for j in range(2,By+1):
        if ss[i][j]:
            continue
        dp[i][j]=dp[i-1][j]+dp[i][j-1]
print(dp[Bx][By])