#include <bits/stdc++.h>
using namespace std;
const int N = 1000;
const int dx[] = {-1, 0, 0, 1};
const int dy[] = {0, -1, 1 , 0};
int a, b, n, m, best_so_far_con, best_so_far_exp, no_of_operations, no_of_touched, min_comp, max_comp;
int mat[N][N], l[N], used[N][N] , on[N][N];
void readData()
{
//freopen("maxComp.in" , "r" , stdin);
//freopen("maxComp.out" , "w" , stdout);
scanf("%d" , &n);
scanf("%d" , &m);
assert(1 <= n && n <= 1000 && 1 <= m && m <= 1000);
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m ; ++j)
{
scanf("%d" , &mat[i][j]);
assert(0 <= mat[i][j] && mat[i][j] <= 1000000000);
}
}
int getValue()
{
int ret = -1;
for (int i = 0 ; i < n ; ++i)
{
for (int j = 0 ; j < m ; ++j)
if (i > 0)
{
if (j > 0)
l[j] = min(min(l[j] , l[j - 1]) , mat[i][j] - i - j);
else l[j] = min(l[j] , mat[i][j] - i - j);
}
else
{
if (j > 0)
l[j] = min(l[j - 1] , mat[i][j] - i - j);
else l[j] = mat[i][j] - i - j;
}
for (int j = 0 ; j < m ; ++j)
ret = max(ret , mat[i][j] - i - j - l[j] - 1);
}
return ret;
}
void solverNM()
{
int best_so_far = getValue();
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m / 2 ; ++j)
swap(mat[i][j] , mat[i][m - 1 - j]);
best_so_far = max(best_so_far , getValue());
for (int i = 0 ; i < n / 2 ; ++i)
for (int j = 0 ; j < m ; ++j)
swap(mat[n - 1 - i][j] , mat[i][j]);
best_so_far = max(best_so_far , getValue());
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m / 2 ; ++j)
swap(mat[i][j] , mat[i][m - 1 - j]);
best_so_far = max(best_so_far , getValue());
printf("%d\n" , best_so_far);
}
int abval(int x)
{
if (x < 0) return -x;
return x;
}
void solverNNMM()
{
int best_so_far = -1;
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m ; ++j)
for (int x = 0 ; x < n ; ++x)
for (int y = 0 ; y < m ; ++y)
{
int k = mat[x][y] - mat[i][j] - abval(x - i) - abval(y - j) - 1;
best_so_far = max(best_so_far , k);
}
printf("%d\n" , best_so_far);
}
void go(int i , int j , int a , int b , int cnt , int limit)
{
if (cnt > limit) return;
no_of_operations++;
best_so_far_con = max(best_so_far_con , b-a-cnt);
for (int p = 0 ; p < 4 ; ++p)
if (0 <= i + dx[p] && i + dx[p] < n && 0 <= j + dy[p] && j + dy[p] < m && !used[i + dx[p]][j + dy[p]])
{
used[i + dx[p]][j + dy[p]] = 1;
go(i + dx[p] , j + dy[p] , min(a , mat[i + dx[p]][j + dy[p]]) , max(b , mat[i + dx[p]][j + dy[p]]) , cnt+1 , limit);
used[i + dx[p]][j + dy[p]] = 0;
}
}
void solverconNM(int limit)
{
best_so_far_con = -1;
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m ; ++j)
{
used[i][j] = 1;
go(i , j , mat[i][j] , mat[i][j] , 1 , limit);
used[i][j] = 0;
}
printf("%d\n" , best_so_far_con);
//printf("No of operations : %d\n", no_of_operations);
}
void check(int i , int j)
{
no_of_touched++;
min_comp = min(min_comp , mat[i][j]);
max_comp = max(max_comp , mat[i][j]);
for (int p = 0 ; p < 4 ; ++p)
if (0 <= i + dx[p] && i + dx[p] < n && 0 <= j + dy[p] && j + dy[p] < m && on[i + dx[p]][j + dy[p]] && !used[i + dx[p]][j + dy[p]])
{
used[i + dx[p]][j + dy[p]] = 1;
check(i + dx[p] , j + dy[p]);
}
}
void solverexpNM()
{
best_so_far_exp = -1;
for (int mask = 1 ; mask < (1 << (n * m)) ; ++mask)
{
int cnt = 0;
for (int i = 0 ; i < n ; ++i)
for (int j = 0 ; j < m ; ++j)
{
used[i][j] = 0;
if (mask & (1 << (i * m + j)))
{
cnt++;
a = i, b = j;
on[i][j] = 1;
}
else on[i][j] = 0;
}
no_of_touched = 0;
min_comp = mat[a][b];
max_comp = mat[a][b];
used[a][b] = 1;
check(a , b);
if (no_of_touched == cnt)
best_so_far_exp = max(best_so_far_exp , max_comp-min_comp-cnt);
}
printf("%d\n", best_so_far_exp);
}
int main()
{
readData();
solverNM();
//solverNNMM();
//solverconNM(20);
//solverexpNM();
return 0;
}
