#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);
}

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 = 1000000000;
    // 最小カット
    mf_graph<ll> graph(2 * H * W + 2);
    for (ll j = 0; j < W; j++){
        graph.add_edge(2 * H * W, j, INF);
        graph.add_edge(H * W + (H - 1) * W + j, 2 * H * W + 1, INF);
    }
    for (ll j = 0; j < W; j++){
        graph.add_edge(j, H * W + W + j, INF);
        graph.add_edge(H * W + j, j, INF);
        graph.add_edge((H - 1) * W + j, H * W + (H - 2) * W + j, INF);
        graph.add_edge(H * W + (H - 1) * W + j, (H - 1) * W + j, INF);
    }
    for (ll i = 1; i < H - 1; i++){
        for (ll j = 0; j < W; j++){
            if (A[i][j] != -1){
                graph.add_edge(i * W + j + H * W, i * W + j, A[i][j]);
            }
            else{
                graph.add_edge(i * W + j + H * W, i * W + j, INF);
            }
            graph.add_edge(i * W + j, (i - 1) * W + H * W + j, INF);
            graph.add_edge(i * W + j, (i + 1) * W + H * W + j, INF);
            if (j > 0){
                graph.add_edge(i * W + j, i * W + H * W + (j - 1), INF);
            }
            if (j < W - 1){
                graph.add_edge(i * W + j, i * W + H * W + (j + 1), INF);
            }
        }
    }
    ll fl = graph.flow(2 * H * W, 2 * H * W + 1);
    if (fl >= INF){
        cout << -1 << endl;
    }
    else{
        cout << fl << endl;
    }
}