import math
import random
def q(w,e):
    if (abs(w-c)+abs(e-d)==3 and w!=c and e!=d) or (w==c and e==d):
        return 0
    else:
        return 1
def f(i,j):
    if i==j==0:
        return 1
    else:
        if i>0 and j>0 :
            if q(i-1,j) and q(i,j-1):
                return f(i,j-1)+f(i-1,j)
            elif q(i-1,j):
                return f(i-1,j)
            elif q(i,j-1):
                return f(i,j-1)
        elif i>0 and q(i-1,j):
            return f(i-1,j)
        elif j>0 and q(i,j-1):
            return f(i,j-1)
    return 0
a,b,c,d=map(int,input().split())
s=f(a,b)
print(s)