#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <cmath>
#include <cassert>
#include <ctime>
#include <utility>
#include <random>
#include <tuple>
#include <bitset>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int,int>
#define pil pair<int,ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define vvpii vector<vector<pair<int,int>>>
#define vvpll vector<vector<pair<ll,ll>>>

template<typename T> void debug(T e){
    cerr << e << endl;
}

template<typename T> void debug(vector<T> &v){
    rep(i, v.size()){
        cerr << v[i] << " ";
    }
    cerr << endl;
}

template<typename T> void debug(vector<vector<T>> &v){
    rep(i, v.size()){
        rep(j, v[i].size()){
            cerr << v[i][j] << " ";
        }
        cerr << endl;
    }
}

template<typename T> void debug(vector<pair<T, T>> &v){
    rep(i,v.size()){
        cerr << v[i].first << " " << v[i].second << endl;
    }
}

template<typename T> void debug(set<T> &st){
    for (auto itr = st.begin(); itr != st.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(multiset<T> &ms){
    for (auto itr = ms.begin(); itr != ms.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(map<T, T> &mp){
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out(){
    cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
    cerr << H << " ";
    debug_out(T...);
}

ll my_pow(ll x, ll n, ll mod){
    //　繰り返し二乗法．x^nをmodで割った余り．
    ll ret;
    if (n == 0){
        ret = 1;
    }
    else if (n % 2 == 1){
        ret = (x * my_pow((x * x) % mod, n / 2, mod)) % mod;
    }
    else{
        ret = my_pow((x * x) % mod, n / 2, mod);
    }
    return ret;
}

ll inv(ll x, ll mod){
    return my_pow(x, mod - 2, mod);
}

void dijkstra(vvpll &graph, ll v, vl &dist){
    priority_queue<pll, vpll, greater<pll>> pque;
    pque.push(pll(0, v));
    dist[v] = 0;
    while(pque.size()){
        pll p = pque.top();
        pque.pop();
        if (dist[p.second] != p.first){
            continue;
        }
        for (auto x: graph[p.second]){
            if (dist[x.first] > dist[p.second] + x.second){
                dist[x.first] = dist[p.second] + x.second;
                pque.push(pll(dist[x.first], x.first));
            }
        }
    }
}


int main(){
    ll H, W;
    cin >> H >> W;
    vvl A(H, vl(W));
    for (ll i = 1; i < H - 1; i++){
        for (ll j = 0; j < W; j++){
            cin >> A[i][j];
        }
    }
    ll INF = 100000000000000;
    // 最短経路問題？
    vector<ll> dist(H * W + 2, INF);
    dist[H * W] = 0;
    vector<vector<pll>> graph(H * W + 2, vpll(0));
    for (ll i = 1; i < H - 1; i++){
        if (A[i][0] != -1){
            graph[H * W].push_back(pll(i * W, A[i][0]));
        }
    }
    for (ll i = 1; i < H - 1; i++){
        if (A[i][W - 1] != -1){
            graph[i * W + (W - 1)].push_back(pll(H * W + 1, 0));
        }
    }
    for (ll i = 1; i < H - 1; i++){
        for (ll j = 0; j < W; j++){
            if (A[i][j] == -1){
                continue;
            }
            if (A[i - 1][j] != -1){
                graph[i * W + j].push_back(pll((i - 1) * W + j, A[i - 1][j]));
            }
            if (A[i + 1][j] != -1){
                graph[i * W + j].push_back(pll((i + 1) * W + j, A[i + 1][j]));
            }
            if (j > 0){
                if (A[i][j - 1] != -1){
                    graph[i * W + j].push_back(pll(i * W + j - 1, A[i][j - 1]));
                }
            }
            if (j < W - 1){
                if (A[i][j + 1] != -1){
                    graph[i * W + j].push_back(pll(i * W + j + 1, A[i][j + 1]));
                }
            }
            if (j > 0){
                if (A[i - 1][j - 1] != -1){
                    graph[i * W + j].push_back(pll((i - 1) * W + j - 1, A[i - 1][j - 1]));
                }
                if (A[i + 1][j - 1] != -1){
                    graph[i * W + j].push_back(pll((i + 1) * W + j - 1, A[i + 1][j - 1]));
                }
            }
            if (j < W - 1){
                if (A[i - 1][j + 1] != -1){
                    graph[i * W + j].push_back(pll((i - 1) * W + j + 1, A[i - 1][j + 1]));
                }
                if (A[i + 1][j + 1] != -1){
                    graph[i * W + j].push_back(pll((i + 1) * W + j + 1, A[i + 1][j + 1]));
                }
            }
        }
    }
    //dijkstra(graph, H * W, dist);
    debug(dist);
    if (dist[H * W + 1] == INF){
        cout << -1 << endl;
    } 
    else{
        cout << dist[H * W + 1] << endl;
    }
}