code forces E A rectangle

 A rectangle

time limit per test

0.5 seconds

memory limit per test

64 megabytes

input

standard input

output

standard output

Developing tools for creation of locations maps for turn-based fights in a new game, Petya faced the following problem.

A field map consists of hexagonal cells. Since locations sizes are going to be big, a game designer wants to have a tool for quick filling of a field part with identical enemy units. This action will look like following: a game designer will select a rectangular area on the map, and each cell whose center belongs to the selected rectangle will be filled with the enemy unit.

More formally, if a game designer selected cells having coordinates (x1, y1) and (x2, y2), where x1 ≤ x2 and y1 ≤ y2, then all cells having center coordinates (x, y) such that x1 ≤ x ≤ x2 and y1 ≤ y ≤ y2 will be filled. Orthogonal coordinates system is set up so that one of cell sides is parallel to OX axis, all hexagon centers have integer coordinates and for each integer x there are cells having center with such xcoordinate and for each integer y there are cells having center with such y coordinate. It is guaranteed that difference x2 - x1 is divisible by 2.

Working on the problem Petya decided that before painting selected units he wants to output number of units that will be painted on the map.

Help him implement counting of these units before painting.

Input

The only line of input contains four integers x1, y1, x2, y2 ( - 109 ≤ x1 ≤ x2 ≤ 109,  - 109 ≤ y1 ≤ y2 ≤ 109) — the coordinates of the centers of two cells.

Output

Output one integer — the number of cells to be filled.

Examples

input

1 1 5 5

output

13

题意：求题目给出的对角点所形成的矩形所包含的六边形中心的个数！

   可以发现所有的中心点都在横纵坐标奇偶相等的点处！

  这样就是求在矩形区域内横纵坐标相等的点的个数！

  AC-code

#include<stdio.h>int main(){__int64  x1,x2,y2,y1;while(scanf("%I64d%I64d%I64d%I64d",&x1,&y1,&x2,&y2)!=EOF){    __int64 x=x2-x1,y=y2-y1;    printf("%I64d\n",(x-x/2)*(y-y/2)+(x/2)*(y/2));}return  0;}