fn run() {
    input! {
        h: usize,
        w: usize,
        a: [[i64; w]; h],
    }
    let inf = std::i64::MAX / 2;
    let mut dp = vec![vec![vec![inf; w]; h]; 2];
    dp[0][0][0] = 0;
    let mut q = std::collections::BinaryHeap::new();
    q.push((0, 0, 0, 0));
    while let Some((d, p, x, y)) = q.pop() {
        let d = -d;
        if d > dp[p][x][y] {
            continue;
        }
        if p == 1 {
            if dp[0][x][y].chmin(d) {
                q.push((-d, 0, x, y));
            }
            if x + 1 < h && dp[1][x + 1][y].chmin(d + a[x + 1][y]) {
                q.push((-dp[1][x + 1][y], 1, x + 1, y));
            }
        } else {
            if x + 1 < h && dp[1][x + 1][y].chmin(d + a[x][y] + a[x + 1][y]) {
                q.push((-dp[1][x + 1][y], 1, x + 1, y));
            }
            if y > 0 && dp[0][x][y - 1].chmin(d) {
                q.push((-d, 0, x, y - 1));
            }
            if y + 1 < w && dp[0][x][y + 1].chmin(d) {
                q.push((-d, 0, x, y + 1));
            }
        }
    }
    println!("{}", dp[0][h - 1].iter().min().unwrap());
}

fn main() {
    run();
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
// ---------- begin chmin, chmax ----------
pub trait ChangeMinMax {
    fn chmin(&mut self, x: Self) -> bool;
    fn chmax(&mut self, x: Self) -> bool;
}

impl<T: PartialOrd> ChangeMinMax for T {
    fn chmin(&mut self, x: Self) -> bool {
        *self > x && {
            *self = x;
            true
        }
    }
    fn chmax(&mut self, x: Self) -> bool {
        *self < x && {
            *self = x;
            true
        }
    }
}
// ---------- end chmin, chmax ----------