#include <bits/stdc++.h>
using namespace std;
using namespace std;
const int MOD = 1e9 + 7;
int fx[] = {-1, +0, +1, +0, +1, +1, -1, -1, +0};
int fy[] = {+0, -1, +0, +1, +1, -1, +1, -1, +0};
template <typename T>
inline T GCD(T a, T b) {
  a = abs(a);
  b = abs(b);
  if (a < b) swap(a, b);
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
template <typename T>
inline T EGCD(T a, T b, T &x, T &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  T x1, y1;
  T d = EGCD(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return d;
}
template <typename T>
inline T LCM(T x, T y) {
  T tp = GCD(x, y);
  if ((x / tp) * 1. * y > 9e18) return 9e18;
  return (x / tp) * y;
}
template <typename T>
inline T BigMod(T A, T B, T M = MOD) {
  T ret = 1;
  while (B) {
    if (B & 1) ret = (ret * A) % M;
    A = (A * A) % M;
    B = B >> 1;
  }
  return ret;
}
template <typename T>
inline T InvMod(T A, T M = MOD) {
  return BigMod(A, M - 2, M);
}
template <typename T>
T scani(T &n) {
  n = 0;
  bool negative = false;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') negative = true;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    n = n * 10 + c - 48;
    c = getchar();
  }
  if (negative) n = ~(n - 1);
  return n;
}
template <typename T>
void write(T n, int type = true) {
  if (n < 0) {
    putchar('-');
    n = -n;
  }
  if (!n) {
    putchar('0');
    if (type == 32)
      putchar(' ');
    else if (type)
      putchar('\n');
    return;
  }
  char buff[22];
  int len = 0;
  while (n) buff[len++] = n % 10 + 48, n /= 10;
  for (int i = len - 1; i >= 0; i--) putchar(buff[i]);
  if (type == 32)
    putchar(' ');
  else if (type)
    putchar('\n');
}
int scans(char *a) {
  int i = 0;
  char c = 0;
  while (c < 33) c = getchar();
  while (c > 33) {
    a[i++] = c;
    c = getchar();
  }
  a[i] = 0;
  return i;
}
const int N = 1003;
long long in[N][N];
long long dp[4][N][N];
string dr[] = {"UL", "DL", "DR", "UR"};
int n, m;
inline bool valid(int x, int y) { return (x >= 0 && y >= 0 && x < n && y < m); }
inline long long ans_me(int k, int x, int y) {
  long long &ret = dp[k][x][y];
  if (ret != -1) return ret;
  ret = 0;
  int dx, dy;
  dx = dy = 1;
  if (dr[k][0] == 'U') dx = -1;
  if (dr[k][1] == 'L') dy = -1;
  if (valid(x + dx, y)) ret = max(ret, ans_me(k, x + dx, y));
  if (valid(x, y + dy)) ret = max(ret, ans_me(k, x, y + dy));
  return ret += in[x][y];
}
int main() {
  memset(dp, -1, sizeof(dp));
  scani(n), scani(m);
  for (int i = (0); i < (n); ++i)
    for (int j = (0); j < (m); ++j) scani(in[i][j]);
  for (int k = (0); k < (4); ++k)
    for (int i = (0); i < (n); ++i)
      for (int j = (0); j < (m); ++j) ans_me(k, i, j);
  long long mx = 0;
  for (int i = (0); i < (n); ++i) {
    for (int j = (0); j < (m); ++j) {
      for (int d = (0); d < (2); ++d) {
        long long tp = 0;
        for (int k = (0); k < (4); ++k) {
          int x = i + fx[(k + d) & 3];
          int y = j + fy[(k + d) & 3];
          if (!valid(x, y)) {
            tp = 0;
            break;
          }
          tp += dp[k][x][y];
        }
        mx = max(mx, tp);
      }
    }
  }
  write(mx);
  return 0;
}
