#include <bits/stdc++.h>
using namespace std;
const int maxn = 1010;
int dp1[maxn][maxn], dp2[maxn][maxn], dp3[maxn][maxn], dp4[maxn][maxn];
int n, m, a[maxn][maxn];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) scanf("%d", &a[i][j]);
  memset(dp1, 0, sizeof(dp1));
  memset(dp2, 0, sizeof(dp2));
  memset(dp3, 0, sizeof(dp3));
  memset(dp4, 0, sizeof(dp4));
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
      dp1[i][j] = a[i][j] + max(dp1[i - 1][j], dp1[i][j - 1]);
  for (int i = 1; i <= n; i++)
    for (int j = m; j >= 1; j--)
      dp2[i][j] = a[i][j] + max(dp2[i - 1][j], dp2[i][j + 1]);
  for (int i = n; i >= 1; i--)
    for (int j = 1; j <= m; j++)
      dp3[i][j] = a[i][j] + max(dp3[i + 1][j], dp3[i][j - 1]);
  for (int i = n; i >= 1; i--)
    for (int j = m; j >= 1; j--)
      dp4[i][j] = a[i][j] + max(dp4[i + 1][j], dp4[i][j + 1]);
  int ans = 0;
  for (int i = 2; i < n; i++)
    for (int j = 2; j < m; j++) {
      ans = max(ans,
                dp1[i - 1][j] + dp2[i][j + 1] + dp3[i][j - 1] + dp4[i + 1][j]);
      ans = max(ans,
                dp1[i][j - 1] + dp2[i - 1][j] + dp3[i + 1][j] + dp4[i][j + 1]);
    }
  printf("%d\n", ans);
  return 0;
}
