#include <bits/stdc++.h>
using namespace std;
const int maxn = 1000 + 10;
int n, m, ans;
int a[maxn][maxn], dp[4][maxn][maxn];
void input() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) cin >> a[i][j];
}
void process() {
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      dp[0][i][j] = a[i][j] + max(dp[0][i - 1][j], dp[0][i][j - 1]);
  for (int i = n; i >= 1; i--)
    for (int j = m; j >= 1; j--)
      dp[1][i][j] = a[i][j] + max(dp[1][i + 1][j], dp[1][i][j + 1]);
  for (int i = n; i >= 1; i--)
    for (int j = 1; j <= m; j++)
      dp[2][i][j] = a[i][j] + max(dp[2][i + 1][j], dp[2][i][j - 1]);
  for (int i = 1; i <= n; i++)
    for (int j = m; j >= 1; j--)
      dp[3][i][j] = a[i][j] + max(dp[3][i - 1][j], dp[3][i][j + 1]);
  for (int i = 2; i <= n - 1; i++)
    for (int j = 2; j <= m - 1; j++)
      ans = max(ans, max(dp[0][i - 1][j] + dp[1][i + 1][j] + dp[2][i][j - 1] +
                             dp[3][i][j + 1],
                         dp[0][i][j - 1] + dp[1][i][j + 1] + dp[2][i + 1][j] +
                             dp[3][i - 1][j]));
  cout << ans << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  input();
  process();
  return 0;
}
