#include "bits/stdc++.h"
#include <climits>
using namespace std;
using ll = long long;
int h, w;
int a[2005][2005];
int minv, maxv;
int t[2005][2005];
int t1[3][2005][2005];
int t2[3][2005][2005];
int t3[3][2005][2005];
int t4[3][2005][2005];
bool check(int thr) {
// cout << "!!" << thr << endl;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
t[i][j] = 0;
if (a[i][j] <= minv + thr) {
t[i][j] += 1;
}
if (a[i][j] >= maxv - thr) {
t[i][j] += 2;
}
// cout << i << " " << j << " " << t[i][j] << endl;
if (t[i][j] == 0) return false;
}
}
for (int k = 1; k <= 2; k++) {
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
t1[k][i][j] = (t[i][j] == k);
t1[k][i][j] = max(t1[k][i][j], max(t1[k][i - 1][j], t1[k][i][j - 1]));
}
}
for (int i = 1; i <= h; i++) {
for (int j = w; j >= 1; j--) {
t2[k][i][j] = (t[i][j] == k);
t2[k][i][j] = max(t2[k][i][j], max(t2[k][i - 1][j], t2[k][i][j + 1]));
}
}
for (int i = h; i >= 1; i--) {
for (int j = 1; j <= w; j++) {
t3[k][i][j] = (t[i][j] == k);
t3[k][i][j] = max(t3[k][i][j], max(t3[k][i + 1][j], t3[k][i][j - 1]));
}
}
for (int i = h; i >= 1; i--) {
for (int j = w; j >= 1; j--) {
t4[k][i][j] = (t[i][j] == k);
t4[k][i][j] = max(t4[k][i][j], max(t4[k][i + 1][j], t4[k][i][j + 1]));
}
}
}
// 1 2
// 3 4
bool flag1 = 1, flag2 = 1, flag3 = 1, flag4 = 1;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
if (t1[1][i][j] == 1 && t4[2][i][j] == 1) flag1 = 0;
if (t2[1][i][j] == 1 && t3[2][i][j] == 1) flag2 = 0;
if (t3[1][i][j] == 1 && t2[2][i][j] == 1) flag3 = 0;
if (t4[1][i][j] == 1 && t1[2][i][j] == 1) flag4 = 0;
}
}
return flag1 || flag2 || flag3 || flag4;
}
int main() {
cin.tie(0)->sync_with_stdio(0);
cin >> h >> w;
minv = INT_MAX;
maxv = INT_MIN;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
cin >> a[i][j];
minv = min(minv, a[i][j]);
maxv = max(maxv, a[i][j]);
}
}
if (minv == maxv) {
cout << 0 << endl;
return 0;
}
int l = 0, r = maxv - minv;
while (l <= r) {
int d = (l + r) / 2;
if (check(d)) {
r = d - 1;
}
else {
l = d + 1;
}
}
cout << l << endl;
}
