#include <bits/stdc++.h>
using namespace std;
int a[1005][1005], dp1[1005][1005], dp2[1005][1005], dp3[1005][1005],
    dp4[1005][1005];
int main() {
  int n, m, cnt = 0;
  scanf("%d%d", &n, &m);
  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++) scanf("%d", &a[i][j]);
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++)
      dp1[i][j] = max(dp1[i - 1][j], dp1[i][j - 1]) + a[i][j];
  }
  for (int i = n; i >= 1; i--) {
    for (int j = m; j >= 1; j--)
      dp2[i][j] = max(dp2[i + 1][j], dp2[i][j + 1]) + a[i][j];
  }
  for (int i = n; i >= 1; i--) {
    for (int j = 1; j <= m; j++)
      dp3[i][j] = max(dp3[i + 1][j], dp3[i][j - 1]) + a[i][j];
  }
  for (int i = 1; i <= n; i++) {
    for (int j = m; j >= 1; j--)
      dp4[i][j] = max(dp4[i - 1][j], dp4[i][j + 1]) + a[i][j];
  }
  for (int i = 2; i < n; i++) {
    for (int j = 2; j < m; j++) {
      cnt = max(cnt,
                dp1[i - 1][j] + dp2[i + 1][j] + dp4[i][j + 1] + dp3[i][j - 1]);
      cnt = max(cnt,
                dp1[i][j - 1] + dp2[i][j + 1] + dp4[i - 1][j] + dp3[i + 1][j]);
    }
  }
  printf("%d\n", cnt);
  return 0;
}
