#include <bits/stdc++.h>
using namespace std;
long long mat[1005][1005];
long long dp[4][1005][1005];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) cin >> mat[i][j];
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      dp[0][i][j] = mat[i][j] + max(dp[0][i][j - 1], dp[0][i - 1][j]);
  for (int i = 1; i <= n; i++)
    for (int j = m; j >= 1; j--)
      dp[1][i][j] = mat[i][j] + max(dp[1][i][j + 1], dp[1][i - 1][j]);
  for (int i = n; i >= 1; i--)
    for (int j = 1; j <= m; j++)
      dp[2][i][j] = mat[i][j] + max(dp[2][i][j - 1], dp[2][i + 1][j]);
  for (int i = n; i >= 1; i--)
    for (int j = m; j >= 1; j--)
      dp[3][i][j] = mat[i][j] + max(dp[3][i][j + 1], dp[3][i + 1][j]);
  long long ans = 0;
  for (int i = 2; i <= n - 1; i++) {
    for (int j = 2; j <= m - 1; j++) {
      ans = max(ans, dp[0][i - 1][j] + dp[3][i + 1][j] + dp[1][i][j + 1] +
                         dp[2][i][j - 1]);
      ans = max(ans, dp[0][i][j - 1] + dp[3][i][j + 1] + dp[1][i - 1][j] +
                         dp[2][i + 1][j]);
    }
  }
  cout << ans << '\n';
  return 0;
}
