#![allow(dead_code, unused_imports, unused_macros, non_snake_case)]

fn main() {
	let [H, W] = read_words::<usize>()[..] else { return };
	let A = (0 .. H).map(|_| read_words::<usize>() ).collect::<Vec<_>>();
	
	let mut colors = vec![vec![None; W]; H];
	colors[0][0] = Some(true);
	colors[H - 1][W - 1] = Some(false);
	
	let mut pq = vec![BinaryHeap::new(); 2];
	for &(i, j, c) in &[(0, 0, 1), (H - 1, W - 1, 0)] {
		neighbor4(i, j, H, W, |i2, j2| {
			if colors[i2][j2].is_none() {
				pq[c].push((Reverse(A[i2][j2]), i2, j2));
			}
		});
	}
	
	let mut ans = 0;
	'main_loop: for t in 1 ..= H * W - 2 {
		let c = t % 2;
		while let Some((_, i, j)) = pq[c].pop() {
			if colors[i][j].is_some() {
				continue;
			}
			let mut fin = false;
			ans += 1;
			colors[i][j] = Some(c == 1);
			neighbor4(i, j, H, W, |i2, j2| {
				if colors[i2][j2].is_none() {
					pq[c].push((Reverse(A[i2][j2]), i2, j2));
				} else if colors[i2][j2] != colors[i][j] {
				    fin = true;
				}
			});
			if fin {
			    break 'main_loop;
			}
			break;
		}
	}
	
	println!("{}", ans);
}

type Int = i64;
const MOD: Int = 1_000_000_007;
const INF: Int = 1_000_000_000;
const YESNO: [&'static str; 2] = ["Yes", "No"];

use std::collections::*;
use std::cmp::Reverse;

fn read_line() -> String { let mut buf = String::new(); std::io::stdin().read_line(&mut buf).ok(); buf }
fn read_words<T: std::str::FromStr>() -> Vec<T> where T::Err: std::fmt::Debug { read_line().split_whitespace().map(|x| T::from_str(x).unwrap() ).collect() }

fn yes() { println!("{}", YESNO[0]); }
fn no() { println!("{}", YESNO[1]); }
fn yesno(c: bool) { println!("{}", if c { YESNO[0] } else { YESNO[1] }); }
fn neighbor4<F: FnMut(usize, usize)>(i: usize, j: usize, h: usize, w: usize, mut f: F) { if i > 0 { (f)(i - 1, j); } if i < h - 1 { (f)(i + 1, j); } if j > 0 { (f)(i, j - 1); } if j < w - 1 { (f)(i, j + 1); } }