A. Tiling with Hexagons

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Several ages ago Berland was a kingdom. The King of Berland adored math. That's why, when he first visited one of his many palaces, he first of all paid attention to the floor in one hall. The floor was tiled with hexagonal tiles.

The hall also turned out hexagonal in its shape. The King walked along the perimeter of the hall and concluded that each of the six sides has a, b, c, a, b and c adjacent tiles, correspondingly.

To better visualize the situation, look at the picture showing a similar hexagon for a = 2, b = 3 and c = 4.

According to the legend, as the King of Berland obtained the values a, b and c, he almost immediately calculated the total number of tiles on the hall floor. Can you do the same?

Input

The first line contains three integers: a, b and c (2 ≤ a, b, c ≤ 1000).

Output

Print a single number — the total number of tiles on the hall floor.

Sample test(s)

input

2 3 4

output

18

解题说明：此题考查几何方面的知识，给出三个值通过规律找出问题的答案。首先可以把原图像分为下面两块：

红色标记部分个数为b*c，上面是一圈(b+c-1)个小块，注意这里a=2，故只有一层，,如果a>2就应该是a-1层。

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;

int main()
{
	int a,b,c;
	scanf("%d %d %d",&a,&b,&c);
	printf("%d\n",b*c+(a-1)*(b+c-1));
	return 0;
}