ax,ay,bx,by = map(int,input().split())
flag = [[0]*(ay+3) for i in range(ax+3)]  #建立一个n*n的矩阵
borad = [[0]*(ay+3) for i in range(ax+3)]  
bx,by = bx+2,by+2
'''标记马及马能到的地方'''
flag[bx][by] = 1
flag[bx+1][by+2] = 1
flag[bx+2][by+1] = 1
flag[bx+2][by-1] = 1
flag[bx-2][by+1] = 1
flag[bx-1][by+2] = 1
flag[bx+1][by-2] = 1
flag[bx-2][by-1] = 1
flag[bx-1][by-2] = 1
'''for 循环通过上方及左边的数字相加最终得到到达B点可通过的路径'''
for x in range(2,ax+3):
    for y in range(2,ay+3):
        if x == 2 and y==2:
            continue
        if x == 2 or y == 2:
            borad[x][y] = 1
            continue
        if flag[x][y] == 1:
            borad[x][y] = 0
            continue
        borad[x][y] = borad[x-1][y] +borad[x][y-1]
print(borad[ax+2][ay+2])