use proconio::input;
use std::cmp::min;

const INF: isize = 1000000000000000000;
fn main() {
    input!{
        h: usize,
        w: usize
    }
    let mut dp = vec![vec![INF; w]; h-2];
    for i in 0..h-2 {
        for j in 0..w {
            input!{
                a: isize
            }
            if a != -1 {
                dp[i][j] = a;
            }
        }
    }
    for j in 1..w {
        for i in 0..h-2 {
            if i == 0 {
                dp[i][j] += min(dp[i][j-1], dp[i+1][j-1]);
            } else if i == h-3 {
                dp[i][j] += min(dp[i-1][j-1], dp[i][j-1]);
            } else {
                dp[i][j] += min(dp[i][j-1], dp[i-1][j-1].min(dp[i+1][j-1]));
            }
        }
    }
    let mut ans = INF;
    for i in 0..h-2 {
        ans = ans.min(dp[i][w-1]);
    }
    if ans == INF {
        println!("-1");
    } else {
        println!("{}", ans);
    }
}