using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (h, w) = (c[0], c[1]);
        var map = NArr(h - 2);
        var INF = int.MaxValue / 2;
        var dp = new int[map.Length][];
        for (var i = 0; i < dp.Length; ++i) dp[i] = Enumerable.Repeat(INF, w).ToArray();
        var q = new PriorityQueue<Pair>(h * w, false);
        for (var i = 0; i < map.Length; ++i) if (map[i][0] > 0)
        {
            q.Enqueue(new Pair(i, 0, map[i][0]));
            dp[i][0] = map[i][0];
        }
        var mx = new int[] { -1, -1, -1, 0, 0, 1, 1, 1 };
        var my = new int[] { -1, 0, 1, -1, 1, -1, 0, 1 };
        while (q.Count > 0)
        {
            var cur = q.Dequeue();
            if (dp[cur.X][cur.Y] != cur.Val) continue;
            for (var i = 0; i < mx.Length; ++i)
            {
                var nx = cur.X + mx[i];
                var ny = cur.Y + my[i];
                if (nx < 0 || nx >= map.Length || ny < 0 || ny >= w) continue;
                if (map[nx][ny] < 0) continue;
                if (dp[nx][ny] <= cur.Val + map[nx][ny]) continue;
                dp[nx][ny] = cur.Val + map[nx][ny];
                q.Enqueue(new Pair(nx, ny, dp[nx][ny]));
            }
        }
        var ans = INF;
        for (var i = 0; i < dp.Length; ++i) ans = Math.Min(ans, dp[i][w - 1]);
        WriteLine(ans == INF ? -1 : ans);
    }
    class Pair : IComparable<Pair>
    {
        public int X;
        public int Y;
        public int Val;
        public Pair(int x, int y, int val)
        {
            X = x; Y = y; Val = val;
        }
        public int CompareTo(Pair b)
        {
            return Val.CompareTo(b.Val);
        }
    }
    class PriorityQueue<T> where T : IComparable<T>
    {
        public T[] List;
        public int Count;
        bool IsTopMax;
        public PriorityQueue(int count, bool isTopMax)
        {
            IsTopMax = isTopMax;
            List = new T[Math.Max(128, count)];
        }
        public void Enqueue(T value)
        {
            if (Count == List.Length)
            {
                var newlist = new T[List.Length * 2];
                for (var i = 0; i < List.Length; ++i) newlist[i] = List[i];
                List = newlist;
            }
            var pos = Count;
            List[pos] = value;
            ++Count;
            while (pos > 0)
            {
                var parent = (pos - 1) / 2;
                if (Calc(List[parent], List[pos], true)) break;
                Swap(parent, pos);
                pos = parent;
            }
        }
        public T Dequeue()
        {
            --Count;
            Swap(0, Count);
            var pos = 0;
            while (true)
            {
                var child = pos * 2 + 1;
                if (child >= Count) break;
                if (child + 1 < Count && Calc(List[child + 1], List[child], false)) ++child;
                if (Calc(List[pos], List[child], true)) break;
                Swap(pos, child);
                pos = child;
            }
            return List[Count];
        }
        bool Calc(T a, T b, bool equalVal)
        {
            var ret = a.CompareTo(b);
            if (ret == 0 && equalVal) return true;
            return IsTopMax ? ret > 0 : ret < 0;
        }
        void Swap(int a, int b)
        {
            var tmp = List[a];
            List[a] = List[b];
            List[b] = tmp;
        }
    }
}