Problem:
Score : 200 points

Problem Statement

Takahashi lives in another world. There are slimes (creatures) of 10000 colors in this world. Let us call these colors Color 1, 2, ..., 10000.

Takahashi has N slimes, and they are standing in a row from left to right. The color of the i-th slime from the left is a_i.
If two slimes of the same color are adjacent, they will start to combine themselves. Because Takahashi likes smaller slimes, he has decided to change the colors of some of the slimes with his magic.

Takahashi can change the color of one slime to any of the 10000 colors by one spell.
How many spells are required so that no slimes will start to combine themselves?

Constraints

2 \leq N \leq 100

1 \leq a_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the minimum number of spells required.

Sample Input 1

5
1 1 2 2 2

Sample Output 1

2

For example, if we change the color of the second slime from the left to 4, and the color of the fourth slime to 5, the colors of the slimes will be 1, 4, 2, 5, 2, which satisfy the condition.

Sample Input 2

3
1 2 1

Sample Output 2

0

Although the colors of the first and third slimes are the same, they are not adjacent, so no spell is required.

Sample Input 3

5
1 1 1 1 1

Sample Output 3

2

For example, if we change the colors of the second and fourth slimes from the left to 2, the colors of the slimes will be 1, 2, 1, 2, 1, which satisfy the condition.

Sample Input 4

14
1 2 2 3 3 3 4 4 4 4 1 2 3 4

Sample Output 4

4

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::str::FromStr;
use std::io::prelude::*;

trait FromFragment: Sized {
    fn from_fragment(s: &str) -> Result<Self, String>;
}

impl FromFragment for String {
    fn from_fragment(s: &str) -> Result<String, String> { Ok(s.to_string()) }
}

// impl FromFragment for bool

macro_rules! impl_from_fragment {
    ( $( $t:ty )* ) => { $(
        impl FromFragment for $t {
            fn from_fragment(s: &str) -> Result<$t, String> {
                <$t>::from_str(s).map_err(|_| {
                    format!("cannot parse \"{}\" as {}", s, stringify!($t))
                })
            }
        }
    )* };
}

impl_from_fragment!(f64 isize i8 i16 i32 i64 usize u8 u16 u32 u64);

trait FromLine: Sized {
    fn from_line(line: &str) -> Result<Self, String>;
}

impl<T: FromFragment> FromLine for T {
    fn from_line(line: &str) -> Result<T, String> {
        T::from_fragment(line.trim_right_matches('\n'))
    }
}

impl<T: FromFragment> FromLine for Vec<T> {
    fn from_line(line: &str) -> Result<Vec<T>, String> {
        let mut result = Vec::new();
        for fragment in line.trim_right_matches('\n').split_whitespace() {
            match T::from_fragment(fragment) {
                Ok(v) => result.push(v),
                Err(msg) => {
                    return Err(format!(
                        "fragment {} of line \"{}\": {}",
                        result.len() + 1, line, msg
                    ))
                }
            }
        }
        Ok(result)
    }
}

macro_rules! impl_from_line_for_tuples {
    ($t:ident $var:ident $count:expr) => ();
    ($t:ident $var:ident $count:expr, $($inner_t:ident $inner_var:ident $inner_count:expr),*) => {
        impl <$t: FromFragment + std::fmt::Display, $($inner_t: FromFragment + std::fmt::Display),*> FromLine for ($t, $($inner_t),*) {
            fn from_line(line: &str) -> Result<( $t, $($inner_t),*), String> {
                let fragments: Vec<&str> =
                    line.trim_right_matches('\n').split_whitespace().collect();
                if fragments.len() != $count {
                    return Err(format!(
                        "line \"{}\" has {} fragments, expected {}",
                        line, fragments.len(), $count
                    ));
                }

                let mut iter = fragments.iter();
                let mut n = 1;
                let $var = <$t>::from_fragment(iter.next().unwrap())
                    .map_err(|msg| {
                        format!("fragment {} of line \"{}\": {}", n, line, msg)
                    })?;
                n += 1;
                $(
                    let $inner_var =
                        <$inner_t>::from_fragment(iter.next().unwrap())
                        .map_err(|msg| {
                            format!("fragment {} of line \"{}\": {}",
                                    n, line, msg)
                        })?;
                    n += 1;
                )*
                Ok(( $var, $($inner_var),* ))
            }
        }
        impl_from_line_for_tuples!($($inner_t $inner_var $inner_count),*);
    }
}

impl_from_line_for_tuples!(T3 x3 3, T2 x2 2, T1 x1 1);

macro_rules! read {
    // Discard a line
    (_) => {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
    };

    // Get a FromLine
    ( $pat:pat = $t:ty ) => {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        let $pat = <$t>::from_line(&line).unwrap();
    };

    // Get FromFragment's
    ( $( $pat:pat = $t:ty ),* ) => {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();

        let mut iter = line.split_whitespace();
        let mut n = 1;
        $(
            let fragment = iter.next().unwrap_or_else(|| {
                panic!(
                    "line \"{}\" has only {} fragment(s), more fragments needed",
                    line, n-1
                )
            });
            let $pat = <$t>::from_fragment(fragment).unwrap_or_else(|msg| {
                panic!("fragment {} of line \"{}\": {}", n, line, msg)
            });
            n += 1;
        )*

        if let Some(fragment) = iter.next() {
            panic!(
                "line \"{}\" not exhasted: only {} fragments read, \
                 leaving the next fragment \"{}\"",
                line, n-1, fragment
            );
        }
    };
}

macro_rules! read_n {
    // Get FromLine's
    ( $( $pat:pat = $t:ty ),* ) => {
        $(
            read!($pat = $t);
        )*
    }
}

macro_rules! read_loop {
    ( $pat:pat = $t:ty; $block:block ) => {
        let stdin = std::io::stdin();
        for line in stdin.lock().lines() {
            let line = line.expect("read from stdin failed");
            let $pat = <$t>::from_line(&line).unwrap();
            $block
        }
    }
}

fn main() {
    read!(_);
    read!(aa = Vec<u8>);
    let mut a = aa[0];
    let mut i = 1;
    let mut l = 1;
    let mut sum = 0;
    while i < aa.len() {
        if (aa[i] == a) {
            l += 1;
        } else {
            a = aa[i];
            sum += l / 2;
            l = 1;
        }
        i += 1;
    }
    sum += l / 2;
    println!("{}", sum);
}