from collections import deque

n, m, x, y = map(int, input().split())
st=set()
ma=[[1,2],[1,-2],[2,1],[2,-1],[-1,2],[-1,-2],[-2,1],[-2,-1]]
zu=[[1,0],[0,1]]
for z in ma:
    st.add((x+z[0],y+z[1]))

def is_valid(b):
    return 0<=b[0]<=n and 0<=b[1]<=m and (b not in st)

q=deque()
q.append((0,0))

res=0
while len(q)>0:
    cur=q.popleft()
    for z in zu:
        cur1=(cur[0]+z[0],cur[1]+z[1])
        if is_valid(cur1):
            if cur1==(n,m):
                res+=1
            else:
                q.append(cur1)

print(res)