pub mod scanner {

    pub struct Scanner {
        buf: Vec<String>,
    }

    impl Scanner {
        pub fn new() -> Self {
            Self { buf: vec![] }
        }

        pub fn new_from(source: &str) -> Self {
            let source = String::from(source);
            let buf = Self::split(source);
            Self { buf }
        }

        pub fn next<T: std::str::FromStr>(&mut self) -> T {
            loop {
                if let Some(x) = self.buf.pop() {
                    return x.parse().ok().expect("");
                }
                let mut source = String::new();
                std::io::stdin().read_line(&mut source).expect("");
                self.buf = Self::split(source);
            }
        }

        fn split(source: String) -> Vec<String> {
            source
                .split_whitespace()
                .rev()
                .map(String::from)
                .collect::<Vec<_>>()
        }
    }
}

use crate::scanner::Scanner;
use std::io::Write;
fn main() {
    let mut scanner = Scanner::new();
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    let t: usize = 1;
    for _ in 0..t {
        solve(&mut scanner, &mut out);
    }
}
fn solve(scanner: &mut Scanner, out: &mut std::io::BufWriter<std::io::StdoutLock>) {
    let n: usize = scanner.next();
    let m: usize = scanner.next();
    let ab = (0..n * m)
        .map(|_| (scanner.next::<usize>(), scanner.next::<usize>()))
        .collect::<Vec<_>>();
    let mut index = vec![vec![0; n + 1]; m + 1];
    for i in 0..n * m {
        let (a, b) = ab[i];
        index[b][a] = i + 1;
    }
    let f = |b: usize, a: usize| -> usize {
        let mut is = Vec::with_capacity(5);
        for ai in a - 4..=a {
            let ai = if ai == n + 1 { 1 } else { ai };
            is.push(index[b][ai]);
        }
        is.sort();
        let mut res = 0;
        let mut p = 5;
        let mut c = 5;
        for i in is {
            if i <= p {
                c -= 1;
                continue;
            }
            let d = i - p;
            let now = (d + c - 1) / c;
            res += now;
            p += c * now;
            c -= 1;
        }
        res
    };
    let mut ans: usize = 1e9 as usize;
    for b in 1..=m {
        for a in 5..=n + 1 {
            ans = ans.min(f(b, a));
        }
    }
    writeln!(out, "{}", ans).unwrap();
}