use std::{cmp::Reverse, collections::BinaryHeap};

use itertools::iproduct;
use proconio::input;

fn main() {
    input! {
        h: usize, w: usize,
        a: [[i32; w]; h - 2],
    }
    let h = h - 2;

    let mut heap = BinaryHeap::new();
    let mut dist = vec![vec![u32::MAX; w]; h];
    for i in 0..h {
        let d = a[i][0] as u32;
        dist[i][0] = d;
        heap.push((Reverse(d), i, 0));
    }

    while let Some((Reverse(d), i, j)) = heap.pop() {
        if d != dist[i][j] {
            continue;
        }

        if j == w - 1 {
            println!("{d}");
            return;
        }

        for (di, dj) in iproduct!(-1..=1, -1..=1) {
            if (di, dj) == (0, 0) {
                continue;
            }
            let ni = i.wrapping_add_signed(di);
            let nj = j.wrapping_add_signed(dj);
            if ni >= h || nj >= w {
                continue;
            }
            let nd = d.saturating_add(a[ni][nj] as u32);
            if dist[ni][nj] > nd {
                dist[ni][nj] = nd;
                heap.push((Reverse(nd), ni, nj));
            }
        }
    }

    println!("-1");
}