#include <bits/stdc++.h>
using namespace std;
const int INF = (1 << 21);
const int MAX = 100000;
const int MAX_V = 10000;
struct edge {
  int to, cap, cost, rev;
};
int V;
vector<edge> G[MAX_V];
int h[MAX_V];
int dist[MAX_V];
int prevv[MAX_V], preve[MAX_V];
void init() {
  for (int i = 0; i < MAX_V; i++) {
    G[i].clear();
  }
}
void add_edge(int from, int to, int cap, int cost) {
  G[from].push_back((edge){to, cap, cost, (int)G[to].size()});
  G[to].push_back((edge){from, 0, -cost, (int)G[from].size() - 1});
}
int min_cost_flow(int s, int t, int f) {
  int res = 0;
  fill(h, h + V, 0);
  while (f > 0) {
    priority_queue<pair<int, int>, vector<pair<int, int> >,
                   greater<pair<int, int> > >
        que;
    fill(dist, dist + V, INF);
    dist[s] = 0;
    que.push(pair<int, int>(0, s));
    while (!que.empty()) {
      pair<int, int> p = que.top();
      que.pop();
      int v = p.second;
      if (dist[v] < p.first) continue;
      for (int i = 0; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]) {
          dist[e.to] = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.push(pair<int, int>(dist[e.to], e.to));
        }
      }
    }
    if (dist[t] == INF) {
      return -1;
    }
    for (int v = 0; v < V; v++) h[v] += dist[v];
    int d = f;
    for (int v = t; v != s; v = prevv[v]) {
      d = min(d, G[prevv[v]][preve[v]].cap);
    }
    f -= d;
    res += d * h[t];
    for (int v = t; v != s; v = prevv[v]) {
      edge &e = G[prevv[v]][preve[v]];
      e.cap -= d;
      G[v][e.rev].cap += d;
    }
  }
  return res;
}
int H, W;
int A[222][222];
int getId(int x, int y) { return y * W + x; }
int dx[] = {0, 1};
int dy[] = {1, 0};
int main() {
  cin >> H >> W;
  V = H * W * 2;
  int T = H * W;
  init();
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      cin >> A[j][i];
      for (int k = 0; k < 2; k++) {
        int nx = j + dx[k], ny = i + dy[k];
        if (nx >= W || ny >= H) continue;
        add_edge(getId(j, i) + T, getId(nx, ny), INF, 0);
      }
      add_edge(getId(j, i), getId(j, i) + T, 1, -A[j][i]);
      add_edge(getId(j, i), getId(j, i) + T, INF, 0);
    }
  }
  int res = -min_cost_flow(0, V - 1, 2);
  cout << res << endl;
}
