#include <bits/stdc++.h>
#define DIM 2010
#define INF 2000000000
using namespace std;
int a[DIM][DIM],b[DIM][DIM],viz[DIM][DIM];
struct idk{
int val,l,c;
} v[DIM*DIM];
deque <pair<int,int> > c;
int di[] = {-1,1,0,0};
int dj[] = {0,0,-1,1};
int n,m,i,j,sol,mini,maxi,k;
int verif (int val){
/// toate valorile < maxi - val trb puse in zona minimelor
for (int i=1;i<=n;i++)
for (int j=1;j<=m;j++)
viz[i][j] = 0;
for (int i=1;i<=k;i++){
if (v[i].val >= maxi - val)
break;
int lin = v[i].l, col = v[i].c;
if (viz[lin][col])
continue;
c.clear();
c.push_back(make_pair(lin,col));
viz[lin][col] = 1;
while (!c.empty()){
int ic = c.front().first;
int jc = c.front().second;
c.pop_front();
for (int dir=0;dir<=3;dir++){
int iv = ic + di[dir];
int jv = jc + dj[dir];
if (iv >= lin && iv <= n && jv >= 1 && jv <= col && !viz[iv][jv]){
viz[iv][jv] = 1;
c.push_back(make_pair(iv,jv));
}}}}
int maxim = 0, maxim2 = 0, minim = INF, minim2 = INF;
for (int i=1;i<=n;i++)
for (int j=1;j<=m;j++){
if (viz[i][j]){
minim = min (minim,a[i][j]);
maxim = max (maxim,a[i][j]);
} else {
minim2 = min (minim2,a[i][j]);
maxim2 = max (maxim2,a[i][j]);
}}
if (max (maxim - minim, maxim2 - minim2) > val)
return 0;
return 1;
}
void solve (){
int st = 0, dr = maxi - mini, val;
while (st <= dr){
int mid = (st+dr)>>1;
if (verif (mid)){
val = mid;
dr = mid-1;
} else st = mid+1;
}
sol = min (sol,val);
}
inline int cmp (idk a, idk b){
return a.val < b.val;
}
void roteste(){
for (i=1;i<=n;i++)
for (j=1;j<=m;j++)
b[m-j+1][i] = a[i][j];
swap (n,m);
k = 0;
for (i=1;i<=n;i++)
for (j=1;j<=m;j++){
a[i][j] = b[i][j];
v[++k] = {a[i][j],i,j};
}
sort (v+1,v+k+1,cmp);
}
int main (){
//ifstream cin ("date.in");
//ofstream cout ("date.out");
cin>>n>>m;
mini = INF;
for (i=1;i<=n;i++)
for (j=1;j<=m;j++){
cin>>a[i][j];
mini = min (mini,a[i][j]);
maxi = max (maxi,a[i][j]);
v[++k] = {a[i][j],i,j};
}
sort (v+1,v+k+1,cmp);
sol = INF;
solve();
roteste();
solve();
roteste();
solve();
roteste();
solve();
cout<<sol;
return 0;
}
