Problem:
 Score : 100 points    Problem Statement There are H rows and W columns of white square cells.  You will choose h of the rows and w of the columns, and paint all of the cells contained in those rows or columns.  How many white cells will remain?  It can be proved that this count does not depend on what rows and columns are chosen.      Constraints  All values in input are integers.  1 \leq H, W \leq 20  1 \leq h \leq H  1 \leq w \leq W         Input Input is given from Standard Input in the following format:  H  W  h  w       Output Print the number of white cells that will remain.        Sample Input 1 3 2
2 1      Sample Output 1 1  There are 3 rows and 2 columns of cells. When two rows and one column are chosen and painted in black, there is always one white cell that remains.       Sample Input 2 5 5
2 3      Sample Output 2 6       Sample Input 3 2 4
2 4      Sample Output 3 0

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

ans = (H-h) * (W-w)
print(ans)

Solution (Python):
import numpy as np

H, W = map(int, input().split())
h, w = map(int, input().split())

table = np.array(np.ones((H, W)))
table[:h] = 0
table[:,:w] = 0
print(int(np.sum(table)))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print(H * W - H * w - h * W + h * w)

Solution (Python):


import sys

def parse_input(lines_as_string = None):


    lines = []
    if lines_as_string is None:
        lines.append(input())
        lines.append(input())
    else:
        lines = [e for e in lines_as_string.split("\n")][1:-1]
 
    tokens = lines[0].split(" ")
    width = int(tokens[0])
    height = int(tokens[1])
    tokens = lines[1].split(" ")
    w = int(tokens[0])
    h = int(tokens[1])

    return (width, height, w, h)


def solve(width, height, w, h):


    return (width - w) * (height - h)

def main():
    

    print("%s" % solve(*parse_input()))

if __name__ == '__main__':

    main()

Solution (Python):

"""
Created on Sat Mar  9 19:52:16 2019

@author: USER
"""

H,W = [int(s) for s in input().split(' ')]
h,w = [int(s) for s in input().split(' ')]
print((H-h)*(W-w))

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())

ans = H*W - (h*W + w*H - h*w )

print(ans)

Solution (Python):
A = list(map(int, input().split())) 
B = list(map(int, input().split()))


print((A[0]-B[0])*(A[1]-B[1]))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

menseki = H * W
kaburi = h * w
a = H * w
b = W * h

x = a + b - kaburi
print(menseki - x)

Solution (Python):
H, W = list(map(int, input().split()))
h, w = list(map(int, input().split()))
print(H * W - (W * h + H * w - h * w))

Solution (Python):
inData1 = input().split(' ')
inData2 = input().split(' ')
sMasu = int(inData1[0]) * int(inData1[1])

sMasu -= int(inData1[1]) * int(inData2[0])
sMasu -= (int(inData1[0]) - int(inData2[0])) * int(inData2[1])

print(sMasu)

Solution (Python):
H,W = map(int,input().split())
a,b = map(int,input().split())
sums = H*b+W*a
sa = a*b
anser = (H*W)-(sums-sa)
print(anser)

Solution (Python):

H, W = map(int, input().split())
h, w = map(int, input().split())

print(H*W-h*W-w*H+w*h)

Solution (Python):
A, B = map(int, input().split())
a, b =map(int, input().split())

print( (A-a)*(B-b))

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print((H-h)*(W-w))

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())

a=0
b=0

a=h*W
b=(w*H)-(h*w)

print((H*W)-(a+b))

Solution (Python):
H, W = [int(x) for x in input().split()]
h, w = [int(x) for x in input().split()]

print((H-h)*(W-w))

Solution (Python):
a = input().split()
b = input().split()

H = int(a[0])
W = int(a[1])
h = int(b[0])
w = int(b[1])

gridAll = H*W
gridRemain = gridAll

gridRemain -= h*W
gridRemain -= w*H
gridRemain += h*w

print(gridRemain)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
white1=h*W 
white2=w*(H-h)

print(H*W-white1-white2)

Solution (Python):
H, W = map(int, input().split(' '))
h, w = map(int, input().split(' '))
print (H*W - (h*W + w*H) + h*w)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
result = (H - h) * W - (H - h) * w
print(result)

Solution (Python):
h, w = map(int, input().split())
y, x = map(int, input().split())

print(h * w - h * x - w * y + x * y)

Solution (Python):
H, W = [int(i) for i in input().split()]
h, w = [int(i) for i in input().split()]

print(H*W - h*W - w*H + h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
total = H*W
line = H * w
row = h * W
double = h * w
white = total - (line + row - double)
print(white)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H - h) * (W - w))

Solution (Python):
a,b=[int(x)for x in input().split()]
c,d=[int(x)for x in input().split()]
print((a-c)*(b-d))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H * W - h * W - w * H + h * w)

Solution (Python):

import sys

import heapq
import re
import bisect
import random
import math
import itertools
from collections import defaultdict, deque
from copy import deepcopy
from decimal import *

H, W= map(int, input().split())
h, w = map(int, input().split())

print(H * W - ((h * W) + (w * (H - h))))

Solution (Python):
h, w = map(int, input().split())
Height, Width = map(int, input().split())
print(h*w - Height*w - Width*(h - Height))

Solution (Python):
W, H = [int(_) for _ in input().split()]
w, h = [int(_) for _ in input().split()]


ans = W*H -(h*W + w*H) + h*w

print(ans)

Solution (Python):
base_row, base_cul = (int(i) for i in input().split())
row, cul = (int(i) for i in input().split())

all = base_row * base_cul



row_deli = row * base_cul



col_deli = cul * base_row



jufuku = row * cul





print(all - (row_deli + col_deli - jufuku))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H - h) * (W - w))

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())

print(H*W-(h*W+w*H-h*w))

Solution (Python):

def IL(): return list(map(int,input().split()))
def SL(): return input().split()
def I(): return int(input())
def S(): return list(input())
H,W=IL()
h,w=IL()
print((H-h)*(W-w))

Solution (Python):
h0,w0=[int(i) for i in input().split()]
h1,w1=[int(i) for i in input().split()]
print(h0*w0-h1*w0-w1*h0+h1*w1)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
print(H*W - (h*W + w*H - h*w))

Solution (Python):
H, W = map(int, raw_input().split())
h, w = map(int, raw_input().split())
print((H - h) * (W - w))

Solution (Python):
n,m = map(int,input().split())
a,b = map(int,input().split())
x,n = n*m-a*m,n-a
print(x-n*b)

Solution (Python):

H,W = map(int,input().split())
h,w = map(int,input().split())

print((H-h)*(W-w))

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())
ans = H*W - h*W - H*w + h*w
print(ans)

Solution (Python):
def A():
    HW = input().split()
    H = int(HW[0])
    W = int(HW[1])
    hw = input().split()
    h = int(hw[0])
    w = int(hw[1])
    print( (H-h) * (W-w) )
    return 

if __name__ == '__main__':
    A()

Solution (Python):


H, W = (int(i) for i in input().split())
h, w = [int(i) for i in input().split()]

print((H*W)-((H*w)+(W*h)-(h*w)))

Solution (Python):
H, W= map(int, input().split())
h, w= map(int, input().split())

A = h * W
B = H * w

a = H * W - (A + B - h * w)
print(a)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-h*W-H*w+h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H - h) * (W - w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H-h) * (W-w))

Solution (Python):

from collections import defaultdict
from heapq import heappush, heappop
import sys
import math
import bisect
import random
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS():return list(map(list, sys.stdin.readline().split()))
def S(): return list(sys.stdin.readline())[:-1]
def IR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = I()
    return l
def LIR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = LI()
    return l
def SR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = S()
    return l
def LSR(n):
    l = [None for i in range(n)]
    for i in range(n):l[i] = SR()
    return l
mod = 1000000007


h,w = LI()
y,x = LI()
print(h*w-h*x-w*y+y*x)

"""
n,m,c = LI()
b = LI()
a = LIR(n)
ans = 0
for i in range(n):
    d = c
    for k in range(m):
        d += b[k]*a[i][k]
    if d > 0:
        ans += 1
print(ans)
"""




"""
n,m = LI()
v = LIR(n)
v.sort(key = lambda x:x[0])
ans = 0
k = 0
for a,b in v:
    if k+b >= m:
        ans += (m-k)*a
        print(ans)
        quit()
    ans += b*a
    k += b
"""

Solution (Python):
H, W = list(map(int, input().split()))
h, w = list(map(int, input().split()))
print((H - h) * (W - w))

Solution (Python):
x = [int(i) for i in input().split()]
y = [int(i) for i in input().split()]
print(x[0]*x[1]-(x[0]*y[1]+x[1]*y[0]-y[0]*y[1]))

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
print(H*W-h*W-w*H+h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
ans = (H - h) * (W - w)
print(ans)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
print((H-h)*(W-w))

Solution (Python):
H,W = list(map(int,input().split()))
h,w = list(map(int,input().split()))

print(H*W -(h*W + w*(H-h)))

Solution (Python):
H,W = map(int,input().split())

h,w = map(int,input().split())

print(H * W - (W * h + H * w - h * w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print(H*W - W*h - H*w + h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
x = h * W + H * w - h * w
print(H*W - x)

Solution (Python):
a = input().split()
b = input().split()

ans = int(a[0])*int(a[1]) - int(a[0])*int(b[1]) - int(a[1])*int(b[0]) + int(b[0])*int(b[1])
print(ans)

Solution (Python):

import sys
sys.setrecursionlimit(10**9)
input = sys.stdin.readline
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H-h)*(W-w))

Solution (Python):
H,W = map(int,input().split(' '))
h,w = map(int,input().split(' '))

newH = H - h
newW = W - w
ans = newH * newW
print(ans)

Solution (Python):




H, W = map(int, input().split())
h, w = map(int, input().split())


ans = H*W - (h*W + w*H) + h*w
print(ans)

Solution (Python):
inp1 = input().split(' ')
inp1 = [int(i) for i in inp1]
inp2 =  input().split(' ')
inp2 = [int(i) for i in inp2]

H, W = inp1[0], inp1[1]
h, w = inp2[0], inp2[1]

print(H*W - h*W - H*w + h*w )

Solution (Python):
l=[[int(j) for j in input().split()] for i in range(2)]
print(l[0][0]*l[0][1] - l[1][0]*l[0][1] - l[1][1]*l[0][0] + l[1][0]*l[1][1])

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H -h) * (W - w))

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())

y = (H - h) * (W - w)
print(y)

Solution (Python):
def main():
    H, W = map(int, input().split())
    h, w = map(int, input().split())

    print(H*W - (h*W + (H-h)*w))


if __name__ == "__main__":
    main()

Solution (Python):


"""
White Cells
"""

def main():
    """
    全体から塗った分を引く。
    """
    H, W = map(int, input().split())
    h, w = map(int, input().split())
    print((H-h) * (W-w))

if __name__ == '__main__':
    main()

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H - h) * (W - w))

Solution (Python):
H, W = [int(_) for _ in input().split()]
h, w = [int(_) for _ in input().split()]

print((H - h) * (W - w))

Solution (Python):
tmp = [int(i) for i in raw_input().split()]
tmp2 = [int(i) for i in raw_input().split()]

all = tmp[0]*tmp[1]
A = tmp[1]*tmp2[0]

B = tmp[0]*tmp2[1]

C = B - tmp2[0]*tmp2[1]

print(all - A - C)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print((H-h)*(W-w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())


def main():
    print(H * W - h * W - w * H + h * w)
    return


main()

Solution (Python):
tate,yoko = map(int,input().split())
tate_hiku,yoko_hiku = map(int,input().split())
zenbu = tate*yoko
tate_hiku_zenbu = tate_hiku*yoko
yoko_hiku_zenbu = yoko_hiku*tate
kasanari = tate_hiku*yoko_hiku
print(zenbu-tate_hiku_zenbu-yoko_hiku_zenbu+kasanari)

Solution (Python):
H, W = [int(s) for s in input().split(" ")]
h, w = [int(s) for s in input().split(" ")]
print(H * W - (H * w + W * h - w * h))

Solution (Python):
HW = list(map(int, input().split()))
hw = list(map(int, input().split()))

a = HW[0]*HW[1]
b = HW[0]*hw[1] + HW[1]*hw[0]
c = hw[0] * hw[1]
print(a-b+c)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

grid = H*W
cons_grid = H*w + W*h
dup_grid = h*w
ans = grid + dup_grid - cons_grid
print(ans)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-H*w-h*W+h*w)

Solution (Python):
from sys import stdin
h, w = [int(x) for x in stdin.readline().rstrip().split()]
a, b = [int(x) for x in stdin.readline().rstrip().split()]
print(h*w-(a*w+(h-a)*b))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W-h*W-w*H+w*h)

Solution (Python):
import numpy as np
H,W = map(int,input().split())
h,w = map(int,input().split())
data = np.ones([H,W])
for i in range(h):
  data[i,:]=0
for i in range(w):
  data[:,i]=0

print(int(data.sum()))

Solution (Python):
import sys

a = list(map(int, input().split()))
H = a[0]
W = a[1]

a = list(map(int, input().split()))
h = a[0]
w = a[1]


print(H * W - ((W - w) * h) - (H * w) )

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())

print(H*W-(h*W+w*H-h*w))

Solution (Python):
H, W = map(int, input().split(" "))
h, w = map(int, input().split(" "))

print((H - h) * (W - w))

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())

ans = H*W - (H*w+W*h)+1*(h*w)
print(ans)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W-h*W-w*H+h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W - h*W - w*H + h*w)

Solution (Python):
H, W = list(map(int, input().split()))
h, w = list(map(int, input().split()))
print((H - h) * (W - w))

Solution (Python):
W, H =  map(int, input().split())
w, h =  map(int, input().split())

print(W*H - w*H - h*W + w*h)

Solution (Python):
h,w = map(int, input().split())
a,b = map(int, input().split())

print((h-a)*(w-b))

Solution (Python):
H,W=map(int,input().split())
h,omega=map(int,input().split())

print(H*W-(h*W)-(H-h)*omega)

Solution (Python):
def readln():
    return list(map(int, input().split()))


H, W = readln()
h, w = readln()
print((H-h)*(W-w))

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-W*h-(H-h)*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

res = (H-h)*(W-w)
print(res)

Solution (Python):
H,W = input().split(' ')
h,w = input().split(' ')

num = int(H) * int(W)
num -= int(W) * int(h)
num -= int(w) * (int(H) - int(h))

print(num)

Solution (Python):
H, W = [int(elem) for elem in input().split()]
h, w = [int(elem) for elem in input().split()]

out = H*W - h*W - (H-h)*w
if out < 0:
    print(0)
else:
    print(out)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
all = H * W
print(all - (h*W + w * H - h*w))

Solution (Python):
A,B = map(int,input().split())
a,b = map(int,input().split())
print((A-a)*(B-b))

Solution (Python):
h,w = list(map(int,input().split()))
h1,w1 = list(map(int,input().split()))

print((h-h1)*(w-w1))

Solution (Python):
H, W =  map(int, (input().split(' ')))
h, w =  map(int, (input().split(' ')))

print(H*W - (h*W + w*H) + w*h)

Solution (Python):
A,B = input().split()
a,b = input().split()
A = int(A)
B = int(B)
a = int(a)
b = int(b)
print(A*B-a*B-b*A+a*b)

Solution (Python):
h, w = map(int, input().split())
h_black, w_black = map(int, input().split())

print((h-h_black)*(w-w_black))

Solution (Python):
a = list(int(_) for _ in input().split())
b = list(int(_) for _ in input().split())

print(a[0]*a[1]-(a[0]*b[1]+a[1]*b[0]-b[0]*b[1]))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print(H * W - H*w - W*h + h * w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W-h*W-H*w+h*w)

Solution (Python):
x,y = map(int, input().split())
a,b = map(int, input().split())

print((x-a)*(y-b))

Solution (Python):
li1 = list(map(int,input().split()))
li2 = list(map(int,input().split()))
print((li1[0]*li1[1])-(li2[0]*li1[1])-((li2[1]*li1[0])-li2[0]*li2[1]))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W-(W*h+H*w)+(h*w))

Solution (Python):

import numpy as np
H, W = map(int, input().split())
h, w = map(int, input().split())
goban = np.array([[1 for i in range(W)] for j in range(H)])
goban[:h :] = 0
goban[:, :w] = 0
print(np.sum(goban))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H - h) * (W - w))

Solution (Python):
H, W = map(int, input().split())
h ,w = map(int, input().split())

print(H*W - (h * W + w * H - h * w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H-h)*(W-w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H * W) - ((w * H) + (W * h) - (w * h)))

Solution (Python):
a, b = map(int, input().split())
c, d = map(int, input().split())
print((a-c)*(b-d))

Solution (Python):
def solver(hh, ww, h, w):
    return hh * ww - h * ww - w * hh + h * w

if __name__ == '__main__':

    hh,ww = map(int, input().split())
    h,w = map(int, input().split())

    ans = solver(hh, ww, h, w)
    print(ans)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())

a=H-h
b=W-w
print(a*b)

Solution (Python):
H, W = map(int,input().split(' '))
h, w = map(int,input().split(' '))
print(H*W - ((h*W) + (w*(H-h))))

Solution (Python):
a,b = map(int,input().split())

k,l = map(int,input().split())

print(a*b - (l*a+k*b-l*k))

Solution (Python):
n=list(map(int,input().split()))
m=list(map(int,input().split()))
kuro=m[0]*n[1] + m[1]*n[0] -m[0]*m[1]
siro=n[0]*n[1]-kuro
print(siro)

Solution (Python):
H,W = map(int, input().split())

h,w = map(int, input().split())


print(H*W - ((h * W) + (w * H) - w * h))

Solution (Python):
A,B=map(int,input().split())
C,D=map(int,input().split())
print(A*B-D*A-B*C+D*C)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
print(W*H-(h*W+H*w-h*w))

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())

W -= w
H -= h

print(H*W)

Solution (Python):
H, W = map(int,input().split())
h, w = map(int,input().split())

result = H * W - (h * W + w * H - h * w)
print(result)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
bk = (h * W) + (H * w) - (h * w)
print((H*W) - bk)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print(H*W -(h*W + w*H-h*w))

Solution (Python):

"""
Created on Sun Mar  3 20:59:27 2019

@author: doppe
"""
H, W = map(int, input().split())
h, w = map(int, input().split())

num = H * W
num = num - H * w
num = num - (W - w) * h

print(num)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-(h*W+H*w-h*w))

Solution (Python):
import numpy as np

H, W = map(int, input().split())
h, w = map(int, input().split())

mat = np.ones((H, W), dtype=np.int)

for i in range(h):
    mat[i, :] = 0
for j in range(w):
    mat[:, j] = 0

print(np.sum(mat))

Solution (Python):
def main():
  H, W = map(int, input().split(' '))
  h, w = map(int, input().split(' '))
  
  a = H*W
  b = (h * W) + (w * H) - h * w
  print(a - b)
  


main()

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-h*W-(H-h)*w)

Solution (Python):
HW = list(map(int, input().split()))
hw = list(map(int, input().split()))

print((HW[0]-hw[0]) * (HW[1]-hw[1]))

Solution (Python):

H, W = map(int, input().split())
h, w = map(int, input().split())
H -= h
W -= w
ans = H * W
print(ans)

Solution (Python):
H, W  = map(int,input().split())
h, w  = map(int,input().split())

ans = (H-h)*(W-w)
print(ans)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
H * W
ans = H * W - (H * w + W * h - h * w)
print(ans)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-(W*h+H*w-h*w))

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())

ans=H*W-(H*w+W*h)+h*w
print(ans)

Solution (Python):
import sys

l = raw_input().split()
H = int(l[0])
W = int(l[1])
l = raw_input().split()
h = int(l[0])
w = int(l[1])

ret = (H - h)*(W - w)

print(ret)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
print((H - h) * (W - w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W + h*w - H*w - h*W)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H - h) * (W - w))

Solution (Python):
H, W = map(int,input().split())
h, w = map(int,input().split())
sum = H * W
diff = h*W + w * H -h*w
print(sum-diff)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
white = H*W
black = h*(W-w)+w*H
white -= black
print(white)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H * W - h * W - H * w + h * w)

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())


print(H*W-h*W-H*w+h*w)

Solution (Python):
H,W = [int(x) for x in input().split()]
h,w = [int(x) for x in input().split()]
print((H-h)*(W-w))

Solution (Python):
a,b=input().split()
a=int(a)
b=int(b)
c,d=input().split()
c=int(c)
d=int(d)
print(a*b-c*b-a*d+c*d)

Solution (Python):
H, W = (int(i) for i in input().split())
h, w = (int(i) for i in input().split())

print(H*W-(h*W+w*H-h*w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H - h) * (W - w))

Solution (Python):
H,W=map(int,input().split())
h,w=map(int,input().split())
print(H*W-h*W-w*H+h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

ans = (H-h) * W - (w * (H - h))
print(ans)

Solution (Python):
H, W = map(int, raw_input().split())
h, w = map(int, raw_input().split())
res = H * W
res = res - h * W - w * H + w * h
print res

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H - h) * (W - w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print(H*W-(H*w+W*h)+h*w)

Solution (Python):
H, W = [int(x) for x in input().split()]
h, w = [int(x) for x in input().split()]
print(((H-h)*W)-(H-h)*w)

Solution (Python):
a, b = map(int,input().split())
c, d = map(int,input().split())
print(a * b - ((a * d + b * c) - (c * d)))

Solution (Python):
H, W = map(int,input().split())
h,w = map(int,input().split())
ans = (H * W) - (h * W) - (H - h) * w
print(ans)

Solution (Python):
input1 = input()
input2 = input()

W,H = list(map(int, input1.split()))
w,h = list(map(int, input2.split()))

print((W-w)*(H-h))

Solution (Python):
H, W = map(int,input().split())
h, w = map(int,input().split())
a = H-h
b = W-w
print(a*b)

Solution (Python):
H,W = map(int, input().split())
h, w = map(int, input().split())
ans = (H - h) * (W - w)
print(ans)

Solution (Python):


"""
Created on Fri Mar  1 19:29:34 2019

@author: nakamuratakayuki
"""

H, W = tuple(map(int, input().split()))
h, w = tuple(map(int, input().split()))
print(H*W-h*W-H*w+h*w)

Solution (Python):
H,W=map(int, input().split())
h,w=map(int, input().split())
print((H-h)*(W-w))

Solution (Python):
H, W = [int(i) for i in input().split()]
h, w = [int(i) for i in input().split()]
print(H*W - (H*w + W*h - h*w))

Solution (Python):
import sys

def main():
    l1 = sys.stdin.readline()
    lst = l1.split()
    height = int(lst[0])
    width = int(lst[1])

    l2 = sys.stdin.readline()
    lst = l2.split()
    h = int(lst[0])
    w = int(lst[1])

    ans = height * width - h * width - w * height + h * w
    print(ans)

    return 0

if __name__ == '__main__':
    sys.exit(main())

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())

white = H*W
black = h*W + (w*H-w*h)
ans = white - black
print(ans)

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())
x = H*W -h*W -H*w + h*w
print(x)

Solution (Python):
H,W = list(map(int,input().split()))
h,w = list(map(int,input().split()))

ans = h*W + w*H - h*w
print(H*W-ans)

Solution (Python):
H, W = map(int,input().split())
h, w = map(int,input().split())

tb = h*W
yb = w*H
ans = H*W - tb - yb + h*w
print(ans)

Solution (Python):
H , W = map(int,input().split())
h,w = map(int,input().split())
print( (H-h)*(W -w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H * W) - (h * W) - (w * H) + (h * w))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())
print((H*W)-(h*W)-(w*H)+(h*w))

Solution (Python):
H,W=map(int, raw_input().split())
h,w=map(int, raw_input().split())

print H*W-(h*W+w*H-h*w)

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print(H * W - (h * W + H * w - h * w))

Solution (Python):
h, w = (int(i) for i in input().split())
h_p, w_p = (int(i) for i in input().split())

print(h*w-(h*w_p+w*h_p-h_p*w_p))

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())

ans = H*W

ans -= h*W
ans -= w*H
ans += w*h

print(ans)

Solution (Python):
H,W = map(int,input().split())
h,w = map(int,input().split())
allnum = H*W
delnum = h*W + w*H
addnum = h*w
print(allnum - delnum + addnum)

Solution (Python):
H, M = map(int,input().split())
h, m = map(int,input().split())

print(H*M - h*M - H*m + h*m)

Solution (Python):
H,W = map(int, input().split())
h,w = map(int, input().split())

print((H*W)-(h*W)-(H*w)+h*w)

Solution (Python):
l1 = input().split(" ")
l2 = input().split(" ")
print((int(l1[0])-int(l2[0]))*(int(l1[1])-int(l2[1])))

Solution (Python):
H,W=(int(x) for x in input().split())
h,w=(int(x) for x in input().split())
result=H*W-(H*w+h*W-h*w)
print(result)

Solution (Python):
import sys
 
 
H,W = sys.stdin.readline().strip().split()
H = int(H)
W = int(W)
 
h,w = sys.stdin.readline().strip().split()
h = int(h)
w = int(w)

ans = (H-h)*(W-w)
ans = int(ans)
print(ans)

Solution (Python):
import sys






"""Template"""


class IP:
    """
    入力を取得するクラス
    """

    def __init__(self):
        self.input = sys.stdin.readline

    def I(self):
        """
        1文字の取得に使います
        :return: int
        """
        return int(self.input())

    def S(self):
        """
        1文字の取得(str
        :return: str
        """
        return self.input()

    def IL(self):
        """
        1行を空白で区切りリストにします(int
        :return: リスト
        """
        return list(map(int, self.input().split()))

    def SL(self):
        """
        1行の文字列を空白区切りでリストにします
        :return: リスト
        """
        return list(map(str, self.input().split()))

    def ILS(self, n):
        """
        1列丸々取得します(int
        :param n: 行数
        :return: リスト
        """
        return [int(self.input()) for _ in range(n)]

    def SLS(self, n):
        """
        1列丸々取得します（str
        :param n: 行数
        :return: リスト
        """
        return [self.input() for _ in range(n)]

    def SILS(self, n):
        """
        Some Int LineS
        横に複数、縦にも複数
        :param n: 行数
        :return: list
        """
        return [self.IL() for _ in range(n)]

    def SSLS(self, n):
        """
        Some String LineS
        :param n: 行数
        :return: list
        """
        return [self.SL() for _ in range(n)]


class Idea:
    def __init__(self):
        pass

    def HF(self, p):
        """
        Half enumeration
        半分全列挙です
        pの要素の和の組み合わせを作ります。
        ソート、重複削除行います
        :param p: list : 元となるリスト
        :return: list : 組み合わせられた和のリスト
        """
        return sorted(set(p[i] + p[j] for i in range(len(p)) for j in range(i, len(p))))

    def Bfs2(self, a):
        """
        bit_full_search2
        bit全探索の改良版
        全探索させたら2進数のリストと10進数のリストを返す
        :return: list２つ : １個目 2進数(16桁)  2個目 10進数
        """
        
        
        
        value = []
        for i in range(1 << len(a)):
            output = []

            for j in range(len(a)):
                if self.bit_o(i, j):
                    """右からj+1番目のiが1かどうか判定"""
                    
                    output.append(a[j])
            value.append([format(i, 'b').zfill(16), sum(output)])

        value.sort(key=lambda x: x[1])
        bin = [value[k][0] for k in range(len(value))]
        val = [value[k][1] for k in range(len(value))]
        return bin, val

    def S(self, s, r=0, m=-1):
        """
        ソート関係行います。色々な設定あります。
        :param s: 元となるリスト
        :param r: reversするかどうか 0=False 1=True
        :param m: （2次元配列）何番目のインデックスのソートなのか
        :return: None
        """
        r = bool(r)
        if m == -1:
            s.sort(reverse=r)
        else:
            s.sort(reverse=r, key=lambda x: x[m])

    def bit_n(self, a, b):
        """
        bit探索で使います。0以上のときにTrue出します
        自然数だからn
        :param a: int
        :param b: int
        :return: bool
        """
        return bool((a >> b & 1) > 0)

    def bit_o(self, a, b):
        """
        bit探索で使います。1のときにTrue出すよ
        oneで1
        :param a: int
        :param b: int
        :return: bool
        """
        return bool(((a >> b) & 1) == 1)

    def ceil(self, x, y):
        """
        Round up
        小数点切り上げ割り算
        :param x: int
        :param y: int
        :return: int
        """
        return -(-x // y)

    def ave(self, a):
        """
        平均を求めます
        :param a: list
        :return: int
        """
        return sum(a) / len(a)

    def gcd(self, x, y):
        if y == 0:
            return x
        else:
            return self.gcd(y, x % y)


"""ここからメインコード"""


def main():
    
    r, e = range, enumerate
    ip = IP()
    id = Idea()

    """この下から書いてね"""
    H, W = ip.IL()
    h, w = ip.IL()
    print(H*W-(W*h+H*w-(h*w)))




main()

Solution (Python):
H,W =map(int,input().split())
h,w =map(int,input().split())
print(H * W - (h * W +(H- h)* w))

Solution (Python):
hh, ww = map(int,(input().split()))
h, w = map(int,(input().split()))
print(hh*ww-h*ww-w*hh+w*h)

Solution (Python):
H, W = map(int,input().split())
h, w = map(int,input().split())

print(int(H*W*(H-h)/H*(W-w)/W))

Solution (Python):
H, W = map(int, input().split())
h, w = map(int, input().split())

print((H-h)*(W-w))

Solution (Python):
a,b = map(int,input().split())
x,y = map(int,input().split())
print((a-x)*(b-y))

Solution (Python):
H,W=map(int,raw_input().split())
h,w=map(int,raw_input().split())



print (H-h) * (W-w)

Solution (Python):


H,W = map(int,input().split())
h,w = map(int,input().split())

print( (H-h)*(W-w) )