#include <bits/stdc++.h>
using namespace std;
int H; // liczba wierszy
int W; // liczba kolumn
vector<vector<int>> altitude;
vector<vector<int>> occupation;
vector<vector<int>> cnt_x;
vector<vector<int>> cnt_o;
int maxi = 0, mini = 1e9+7;
void occupation_for_delta(int d) {
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) {
const auto& now = altitude[i][j];
bool first = abs(mini - now) <= d;
bool second = abs(maxi - now) <= d;
if (first && second) occupation[i][j] = 0;
else if (first) occupation[i][j] = 1;
else if (second) occupation[i][j] = 2;
else occupation[i][j] = 3;
}
}
}
void count_prefix_sums() {
for (int i=0; i<=H+1; i++) {
cnt_x[i][0] = 0;
cnt_o[i][0] = 0;
}
for (int j=0; j<=W+1; j++) {
cnt_x[0][j] = 0;
cnt_o[0][j] = 0;
}
for (int i=1; i<=H+1; i++) {
for (int j=1; j<=W+1; j++) {
cnt_x[i][j] = cnt_x[i-1][j] + cnt_x[i][j-1] - cnt_x[i-1][j-1];
cnt_o[i][j] = cnt_o[i-1][j] + cnt_o[i][j-1] - cnt_o[i-1][j-1];
if (i <= H && j <= W) {
cnt_x[i][j] += (occupation[i][j] == 1);
cnt_o[i][j] += (occupation[i][j] == 2);
}
}
}
}
int sum(vector<vector<int>>& cnt, int i1, int j1, int i2, int j2) {
if (i1 > i2) swap(i1, i2);
if (j1 > j2) swap(j1, j2);
return cnt[i2][j2] - cnt[i1-1][j2] - cnt[i2][j1-1] + cnt[i1-1][j1-1];
}
bool check_quarter(int ip, int jp) {
for (int i=1; i<=H; i++) for (int j=1; j<=H; j++)
if (occupation[i][j] == 2 && sum(cnt_x, i, j, ip, jp)) return false;
return true;
}
bool check_occupation() {
for (int i=1; i<=H; i++) for (int j=1; j<=W; j++) if (occupation[i][j] == 3) return false;
count_prefix_sums();
if (check_quarter(1,1)) return true;
if (check_quarter(1,W)) return true;
if (check_quarter(H,1)) return true;
if (check_quarter(H,W)) return true;
return false;
}
void print_occupation() {
vector<char> temp = { '.', 'x', 'o', '@' };
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) cout << temp[occupation[i][j]];
cout << '\n';
}
}
void print_prefix_sums() {
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) cout << cnt_x[i][j] << ' ';
cout << '\n';
}
cout << '\n';
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) cout << cnt_o[i][j] << ' ';
cout << '\n';
}
cout << '\n';
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> H >> W;
altitude.assign(H+1, vector<int>(W+1, 0));
occupation.assign(H+1, vector<int>(W+1, 0));
cnt_o.assign(H+2, vector<int>(W+2, 0));
cnt_x.assign(H+2, vector<int>(W+2, 0));
for (int i=1; i<=H; i++) for (int j=1; j<=W; j++) {
cin >> altitude[i][j];
maxi = max(maxi,altitude[i][j]);
mini = min(mini, altitude[i][j]);
}
// int low = 0;
// int high = maxi - mini;
// while (low != high) {
// int mid = (low + high) / 2;
// occupation_for_delta(mid);
// if (check_occupation()) high = mid;
// else low = mid + 1;
// }
// cout << low << '\n';
for (int i=0; i<=maxi-mini; i++) {
occupation_for_delta(i);
if (check_occupation()) {
cout << i << '\n';
return 0;
}
}
}
