const INF: usize = 1usize << 60;

fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<usize> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nm[0];
    let m = nm[1];
    let grid = (0..n).map(|_| {
            let mut a = String::new();
            std::io::stdin().read_line(&mut a).ok();
            let a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
            a
        })
        .collect::<Vec<_>>();

    if n == 1 {
        println!("0");
        return;
    }
    let mut dp = vec![vec![INF; m]; n+1];
    for i in 0..m { dp[0][i] = 0; }
    for i in 0..n {
        let minval = *dp[i].iter().min().unwrap();
        for j in 0..m {
            if i > 0 {
                dp[i+1][j] = dp[i+1][j].min(minval + grid[i-1][j] + grid[i][j]);
            }
            dp[i+1][j] = dp[i+1][j].min(dp[i][j] + grid[i][j]);
        }
    }
    println!("{}", dp[n].iter().min().unwrap());
}