#include <bits/stdc++.h>

using namespace std;
using i64 = int64_t;

template <typename flow_t>
struct Dinic {
  const flow_t INF;

  struct edge {
    int to;
    flow_t cap;
    int rev;
    bool isrev;
    int idx;
  };

  vector<vector<edge> > graph;
  vector<int> min_cost, iter;

  Dinic(int V) : INF(numeric_limits<flow_t>::max()), graph(V) {}

  void add_edge(int from, int to, flow_t cap, int idx = -1) {
    graph[from].emplace_back(
        (edge){to, cap, (int)graph[to].size(), false, idx});
    graph[to].emplace_back(
        (edge){from, 0, (int)graph[from].size() - 1, true, idx});
  }

  bool bfs(int s, int t) {
    min_cost.assign(graph.size(), -1);
    queue<int> que;
    min_cost[s] = 0;
    que.push(s);
    while (!que.empty() && min_cost[t] == -1) {
      int p = que.front();
      que.pop();
      for (auto &e : graph[p]) {
        if (e.cap > 0 && min_cost[e.to] == -1) {
          min_cost[e.to] = min_cost[p] + 1;
          que.push(e.to);
        }
      }
    }
    return min_cost[t] != -1;
  }

  flow_t dfs(int idx, const int t, flow_t flow) {
    if (idx == t) return flow;
    for (int &i = iter[idx]; i < graph[idx].size(); i++) {
      edge &e = graph[idx][i];
      if (e.cap > 0 && min_cost[idx] < min_cost[e.to]) {
        flow_t d = dfs(e.to, t, min(flow, e.cap));
        if (d > 0) {
          e.cap -= d;
          graph[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }

  flow_t max_flow(int s, int t) {
    flow_t flow = 0;
    while (bfs(s, t)) {
      iter.assign(graph.size(), 0);
      flow_t f = 0;
      while ((f = dfs(s, t, INF)) > 0) flow += f;
    }
    return flow;
  }

  void output() {
    for (int i = 0; i < graph.size(); i++) {
      for (auto &e : graph[i]) {
        if (e.isrev) continue;
        auto &rev_e = graph[e.to][e.rev];
        cout << i << "->" << e.to << " (flow: " << rev_e.cap << "/"
             << e.cap + rev_e.cap << ")" << endl;
      }
    }
  }
};

int main() {
  i64 H, W;
  cin >> H >> W;
  Dinic<i64> dinic(H * W);

  auto ind = [&](i64 h, i64 w) { return h * W + w; };
  for (i64 i = 1; i < H - 1; i++) {
    for (i64 j = 0; j < W; j++) {
      i64 A;
      cin >> A;
      if (A == -1) {
        A = 1e9;
      }
      dinic.add_edge(ind(i, j), ind(i + 1, j), A);
      dinic.add_edge(ind(i + 1, j), ind(i, j), A);
      if (j + 1 < W) {
        dinic.add_edge(ind(i, j), ind(i, j + 1), A);
        dinic.add_edge(ind(i, j + 1), ind(i, j), A);
      }
    }
  }
  for (i64 i = 0; i < W; i++) {
    dinic.add_edge(ind(0, i), ind(1, i), 1e9);
    dinic.add_edge(ind(H - 2, i), ind(H - 1, i), 1e9);
    if (i + 1 < W) {
      dinic.add_edge(ind(0, i), ind(0, i + 1), 1e9);
    }
  }
  i64 ans = dinic.max_flow(0, H * W - 1);
  if (1e8 <= ans) {
    cout << -1 << endl;
  } else {
    cout << ans << endl;
  }
  return 0;
}