x1,y1,x2,y2=map(int,input().split())
c=0
l=((y2-y1)//2)+1
if (y2-y1)%2==0:
t=(y2-y1)//2
else:
t=(y2-y1+1)//2
big=(x2-x1)//2+1
if (x2-x1)%2!=0: small=((x2-x1)+1)//2
else: small=(x2-x1)//2
print(t*small+l*big)1217. Minimum Cost to Move Chips to The Same Position | 347. Top K Frequent Elements |
1503. Last Moment Before All Ants Fall Out of a Plank | 430. Flatten a Multilevel Doubly Linked List |
1290. Convert Binary Number in a Linked List to Integer | 1525. Number of Good Ways to Split a String |
72. Edit Distance | 563. Binary Tree Tilt |
1306. Jump Game III | 236. Lowest Common Ancestor of a Binary Tree |
790. Domino and Tromino Tiling | 878. Nth Magical Number |
2099. Find Subsequence of Length K With the Largest Sum | 1608A - Find Array |
416. Partition Equal Subset Sum | 1446. Consecutive Characters |
1618A - Polycarp and Sums of Subsequences | 1618B - Missing Bigram |
938. Range Sum of BST | 147. Insertion Sort List |
310. Minimum Height Trees | 2110. Number of Smooth Descent Periods of a Stock |
2109. Adding Spaces to a String | 2108. Find First Palindromic String in the Array |
394. Decode String | 902. Numbers At Most N Given Digit Set |
221. Maximal Square | 1200. Minimum Absolute Difference |
1619B - Squares and Cubes | 1619A - Square String |