103780: [Atcoder]ABC378 A - Pairing

Problem Statement

There are four balls, and the color of the $i$-th ball is $A_i$.

Find the maximum number of times you can perform this operation: choose two balls of the same color and discard both.

Constraints

• Each of $A_1, A_2, A_3, A_4$ is an integer between $1$ and $4$, inclusive.

Input

The input is given from Standard Input in the following format:

$A_1$ $A_2$ $A_3$ $A_4$

Output

Print the maximum number of times the operation can be performed as an integer.

Sample Input 1

2 1 2 1

Sample Output 1

2

The first and third balls both have color $2$, so you can perform the operation to discard the first and third balls together.

Next, the second and fourth balls both have color $1$, so you can perform the operation to discard the second and fourth balls together.

Hence, you can perform a total of two operations.

Sample Input 2

4 4 4 1

Sample Output 2

1

Sample Input 3

1 2 3 4

Sample Output 3

0

There are cases where you cannot perform the operation even once.

问题陈述

有四个球，第$i$个球的颜色是$A_i$。

找出你可以执行以下操作的最大次数：选择两个颜色相同的球并丢弃它们。

约束条件

• $A_1, A_2, A_3, A_4$每一个都是介于$1$和$4$（包含$1$和$4$）的整数。

输入

输入从标准输入以下格式给出：

$A_1$ $A_2$ $A_3$ $A_4$

输出

以整数形式打印可以执行操作的最大次数。

示例输入 1

2 1 2 1

示例输出 1

2

第一个和第三个球都是颜色$2$，所以你可以执行操作来同时丢弃这两个球。

接下来，第二个和第四个球都是颜色$1$，所以你可以执行操作来同时丢弃这两个球。

因此，你可以总共执行两次操作。

示例输入 2

4 4 4 1

示例输出 2

1

示例输入 3

1 2 3 4

示例输出 3

0

有些情况下，你甚至不能执行一次操作。