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)

#![allow(unused_imports)]
#![allow(dead_code)]
#![allow(unused_must_use)]
use std::io::{stdin, stdout, stderr, Write, BufWriter, BufReader, BufRead};
use std::collections::BinaryHeap;

use util::IterExt;
macro_rules! read_from_line {
    ($inbuf:ident => $($name:ident : $ty:ty),* ) => {
        let mut buf = String::new();
        $inbuf.read_line(&mut buf).unwrap();
        buf.pop();
        let mut words = buf.split_whitespace();
        $(
            let $name:$ty = words.next().unwrap().parse().unwrap();
        )*
    };
}

macro_rules! read_many {
    ($inbuf:ident => $name:ident : $ty:ty) => {
        let $name: Vec<$ty> = strio::read_many_from_line(&mut $inbuf);
    };
}

#[derive(PartialEq, Eq, Debug)]
struct RevOrd<T>(T);

impl<T> PartialOrd for RevOrd<T> where T: PartialOrd {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        other.0.partial_cmp(&self.0)
    }
}

impl<T> Ord for RevOrd<T> where T: Ord {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        other.0.cmp(&self.0)
    }
}

#[derive(Debug)]
struct KV<K, V> {
    k: K,
    v: V
}
impl <K, V> KV<K, V> {
    fn new(k: K, v: V) -> Self {
        KV {k:k, v:v}
    }
}
impl <K, V> PartialEq for KV<K, V> where V: PartialEq {
    fn eq(&self, other: &Self) -> bool {
        self.v.eq(&other.v)
    }
}
impl <K, V> Eq for KV<K, V> where V: Eq { }
impl<K, V> PartialOrd for KV<K, V> where V: PartialOrd {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        self.v.partial_cmp(&other.v)
    }
}
impl<K, V> Ord for KV<K, V> where V: Ord {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.v.cmp(&other.v)
    }
}

#[derive(Debug)]
struct UnionFind {
    tree: Vec<usize>,
}

impl UnionFind {
    fn new(n: usize) -> UnionFind {
        UnionFind { 
            tree: (0..n+1).collect()
        }
    }

    fn root(&mut self, i: usize) -> usize {
        let mut r = i;
        let mut stack = vec![];
        while self.tree[r] != r {
            stack.push(r);
            r = self.tree[r];
        }

        for x in stack {
            self.tree[x] = r
        }
        r
    }

    fn unify(&mut self, i: usize, j: usize) {
        let i = self.root(i);
        let j = self.root(j);
        self.tree[std::cmp::max(i, j)] = std::cmp::min(i, j);
    }

}


fn solve() {
    let cout = stdout();
    let mut cout = BufWriter::new(cout.lock());
    let cin = stdin();
    let mut cin = BufReader::new(cin.lock());

    read_from_line!(cin => n: usize);
    read_many!(cin => xs: usize);
    let mut last = None;
    let mut cnt:usize = 0;
    for x in xs {
        if last == Some(x) {
            last = None;
            cnt += 1;
        } else {
            last = Some(x);
        }
    }
    writeln!(cout, "{}", cnt);
    

}

fn main() {
    let stack_size = 100 * 1024 * 1024;
    let thread = std::thread::Builder::new().stack_size(stack_size);
    thread.spawn(|| solve()).unwrap().join().unwrap();
}

mod util {
    use std;
    use std::ops::{Deref, AddAssign};
    use std::iter::{Once, Chain, Scan};
    use std::borrow::Borrow;

    pub trait IterExt where
        Self: Iterator
    {
        fn scan_init<'a, St : 'a, F : 'a> (self, initial_state: St, f: F) -> Box<Iterator<Item=St> + 'a> /*Chain<Once<St>, Scan<Self, St, F>>*/  where
            Self: Sized + 'a,
            F: FnMut(&mut St, Self::Item) -> Option<St>,
            St: Clone
        {
            Box::new(std::iter::once(initial_state.clone()).chain(self.scan(initial_state, f)))
        }

        fn accum<'a, T> (self, init: T) -> Box<Iterator<Item=T> + 'a> where
            Self: Sized + 'a,
            Self::Item: Borrow<T>,
            T: Clone + AddAssign + 'a,
        {
            Box::new(self.scan_init(init, |sum, x| { *sum += x.borrow().clone(); Some(sum.clone()) }))
        }
    }

    impl<T> IterExt for T where
        T: Iterator
    { }

    pub fn test()
    {
        let v:Vec<i32> = vec![1, 4 ,2];
        for x in v.iter().accum(0) {
            println!("{}", x);
        }
        for x in v.iter().accum(0).accum(0) {
            println!("{}", x);
        }

    }

}

mod strio {
    use std::str::FromStr;
    use std;

    pub fn read_from_line<T, R> (r: &mut R) -> T where
        T: FromStr,
        <T as std::str::FromStr>::Err : std::fmt::Debug,
        R: std::io::BufRead,
    {
        let mut buf = String::new();
        r.read_line(&mut buf).unwrap();
        buf.pop();
        buf.parse().unwrap()
    }

    pub fn read_many_from_line<T, R> (r: &mut R) -> Vec<T> where
        T: FromStr,
        <T as std::str::FromStr>::Err : std::fmt::Debug,
        R: std::io::BufRead,
    {
        let mut buf = String::new();
        r.read_line(&mut buf).unwrap();
        buf.pop();
        buf.split_whitespace().map(|x| x.parse().unwrap()).collect()
    }
}