/*************************************************************************

> File Name: 1084_2.cpp

> Author: dulun

> Mail: dulun@xiyoulinux.org

> Created Time: 2016年03月03日 星期四 20时16分12秒

************************************************************************/

#include<iostream>

#include<stdio.h>

#include<cstring>

#include<cstdlib>

#include<algorithm>

#define LL long long

using namespace std;

const int N = 201;

int dp[N][N][N];

int a[N][N];

int max_4(int a, int b, int c, int d)

{

if(a >= b && a >= c && a >= d) return a;

if(b >= a && b >= c && b >= d) return b;

if(c >= a && c >= b && c >= d) return c;

if(d >= a && d >= c && d >= b) return d;

}

int main()

{

int m, n;

cin>>m>>n;

for(int i = 1; i <= n; i++)

for(int j = 1; j <= n; j++) scanf("%d", &a[i][j]);

int d;

for(int x1 = 1; x1 <= n; x1++)

for(int x2 = 1; x2 <= n; x2++)

for(int k = max(x1, x2)+1; k <= min(x1, x2)+m; k++)

{

if(x1 != x2) d = a[x1][k-x1] + a[x2][k-x2];

else d = a[x1][k-x1];

dp[k][x1][x2] = max(dp[k-1][x1-1][x2], max(dp[k-1][x1][x2-1],max( dp[k-1][x1-1][x2-1], dp[k-1][x1][x2]))) + d;

}

printf("%d\n", dp[m+n][n][n]);

return 0;

}