#include <bits/stdc++.h>
using namespace std;
int m, n, a[1005][1005];
long long int dp[5][1005][1005], x, y, z;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) cin >> a[i][j];
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      dp[1][i][j] = a[i][j] + max(dp[1][i][j - 1], dp[1][i - 1][j]);
    }
    for (int j = m; j >= 1; j--) {
      dp[2][i][j] = a[i][j] + max(dp[2][i][j + 1], dp[2][i - 1][j]);
    }
  }
  for (int i = n; i >= 1; i--) {
    for (int j = 1; j <= m; j++) {
      dp[3][i][j] = a[i][j] + max(dp[3][i][j - 1], dp[3][i + 1][j]);
    }
    for (int j = m; j >= 1; j--) {
      dp[4][i][j] = a[i][j] + max(dp[4][i][j + 1], dp[4][i + 1][j]);
    }
  }
  for (int i = 2; i < n; i++)
    for (int j = 2; j < m; j++) {
      y = max(
          dp[1][i][j - 1] + dp[3][i + 1][j] + dp[4][i][j + 1] + dp[2][i - 1][j],
          dp[1][i - 1][j] + dp[3][i][j - 1] + dp[4][i + 1][j] +
              dp[2][i][j + 1]);
      x = max(x, y);
    }
  cout << x;
  return 0;
}
