#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
#pragma region
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using i128 = __int128;
using u128 = unsigned __int128;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vector<int>>;
using vvll = vector<vector<ll>>;
using vvvi = vector<vector<vector<int>>>;
using vpi = vector<pair<int,int>>;
using vpll = vector<pair<ll,ll>>;
using vs = vector<string>;
using vb = vector<bool>;
using vvb = vector<vector<bool>>;
using pi = pair<int,int>;
using pll = pair<ll,ll>;
template<typename T = int> using spq = priority_queue<T, vector<T>, greater<T>>;
template<typename T = int> using gpq = priority_queue<T>;
#define fi first
#define se second
#define fore(p,a) for (auto p : a)
#define overload4(a,b,c,d,name,...) name
#define rep1(n) for (int i = 0; i < int (n); ++i)
#define rep2(i,n) for (int i = 0; i < int (n); ++i)
#define rep3(i,a,b) for (int i = a; i < int (b); ++i)
#define rep4(i,a,b,c) for (int i = a; i < int (b); i += c)
#define rep(...) overload4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define rrep1(n) for (int i = n; i--;)
#define rrep2(i,n) for (int i = n; i--;)
#define rrep3(i,a,b) for (int i = b; i-- > (a);)
#define rrep4(i,a,b,c) for (int i = (a) + ((b) - (a) - 1) / (c) * (c); i >= (a); i -= c)
#define rrep(...) overload4(__VA_ARGS__,rrep4,rrep3,rrep2,rrep1)(__VA_ARGS__)
#define all(container) begin(container), end(container)
#define rall(container) rbegin(container), rend(container)
#define mvvi(name, row, column) vvi name(row, vi(column))
#define mvvll(name, row, column) vvll name(row, vll(column))
#define mvvb(name, row, column) vvb name(row, vb(column))
#define Max(...) max({__VA_ARGS__})
#define Min(...) min({__VA_ARGS__})
#define fin exit(0)
#define popc __builtin_popcount
#define inrange(x, l, r) ((l) <= (x) && (x) < (r))
#define sq(x) ((x) * (x))
#ifdef LOCAL
template<typename T> string internal_vectostr(vector<T> v) { string ret; for (int i = 0; i < (int) v.size(); i++) ret += (i ? ", " : "") + to_string(v[i]); return ret; }
#define dbg(x) cerr << "[DEBUG] " << __LINE__ << ": " << #x << " = " << x << endl
#define dbv(x) cerr << "[DEBUG] " << __LINE__ << ": " << #x << " = { " << internal_vectostr(x) << " }" << endl
#define tabout(tab, n, m) cout << "[DEBUG]\n"; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) cout << tab[i][j] << ' '; cout << endl; }
#else
template<typename T> void internal_vectostr(vector<T> v) {}
#define dbg(x) ((void) 0)
#define dbv(x) ((void) 0)
#define tabout(tab, n, m) ((void) 0)
#endif
constexpr int INF = 1001001001;
constexpr ll LINF = 1LL << 60;
constexpr double EPS = 1e-10;
const double PI = acos(-1);
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
ll fact(ll x) { return x == 0 ? 1 : x * fact(x - 1); }
ll comb(ll n, ll r) { if (r < 0 || n < r) return 0; ll ret = 1; for (ll i = 1; i <= r; i++) { ret *= n; n--; ret /= i; } return ret; }
int Yes(bool f=1) { cout << (f ? "Yes" : "No") << '\n'; return 0; }
int No() { Yes(0); return 0; }
int YES(bool f=1) { cout << (f ? "YES" : "NO") << '\n'; return 0; }
int NO() { YES(0); return 0; }
int yes(bool f=1) { cout << (f ? "yes" : "no") << '\n'; return 0; }
int no() { yes(0); return 0; }
template<class T> int printvec(vector<T> v) { for (int i = 0; i < (int) v.size(); i++) cout << (i ? " " : "") << v[i]; cout << '\n'; return 0; }
struct IoInit { IoInit() { ios::sync_with_stdio(false); cin.tie(nullptr); cout << setprecision(15) << fixed; cerr << setprecision(15) << fixed; } } io_init;
#pragma endregion

#include<atcoder/maxflow>
int main(){
    int h,w;
    cin>>h>>w;
    mvvi(a,h-2,w);
    rep(h-2)rep(j,w)cin>>a[i][j];
    rep(h-2)rep(j,w)if(a[i][j]==-1)a[i][j]=INF;
    atcoder::mf_graph<ll>g(2*h*w);
    auto pos=[&](int i,int j){return i*w+j;};
    auto in=[](int x){return x;};
    auto out=[&](int x){return h*w+x;};
    rep(h-2)rep(j,w)g.add_edge(in(pos(i+1,j)),out(pos(i+1,j)),a[i][j]);
    rep(h-2)rep(j,w){
        if(j<w-1){
            g.add_edge(out(pos(i+1,j)),in(pos(i+1,j+1)),INF);
            g.add_edge(out(pos(i+1,j+1)),in(pos(i+1,j)),INF);
        }
        if(i<h-3){
            g.add_edge(out(pos(i+1,j)),in(pos(i+2,j)),INF);
            g.add_edge(out(pos(i+2,j)),in(pos(i+1,j)),INF);
        }
    }
    rep(j,w)g.add_edge(0,in(pos(1,j)),INF);
    rep(j,w)g.add_edge(out(pos(h-2,j)),2*h*w-1,INF);
    int res=g.flow(0,2*h*w-1);
    if(res>=INF)cout<<-1<<endl;
    else cout<<res<<endl;
}