#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; i++) for (int j=0; j<=W; j++) cnt_x[i][j] = 0, cnt_o[i][j] = 0;
for (int i=1; i<=H; i++) for (int j=1; j<=W; j++) {
cnt_x[i][j] = cnt_x[i-1][j] + cnt_x[i][j-1] - cnt_x[i-1][j-1] + (occupation[i][j] == 1);;
cnt_o[i][j] = cnt_o[i-1][j] + cnt_o[i][j-1] - cnt_o[i-1][j-1] + (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 x, vector<vector<int>>& cnt, int ip, int jp) {
for (int i=1; i<=H; i++) for (int j=1; j<=W; j++)
if (occupation[i][j] == x && sum(cnt, i, j, ip, jp) > 0) 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();
bool flag_x = (check_quarter(1, cnt_o, 1,1) || check_quarter(1, cnt_o, 1, W) || check_quarter(1, cnt_o, H, 1) || check_quarter(1, cnt_o, H,W));
bool flag_o = (check_quarter(2, cnt_x, 1,1) || check_quarter(2, cnt_x, 1, W) || check_quarter(2, cnt_x, H, 1) || check_quarter(2, cnt_x, H,W));
return flag_x; // && flag_o;
}
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() {
cout << "cnt_x\n";
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) cout << setw(2) << cnt_x[i][j] << ' ';
cout << '\n';
}
cout << '\n';
cout << "cnt_o\n";
for (int i=1; i<=H; i++) {
for (int j=1; j<=W; j++) cout << setw(2) << 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+1, vector<int>(W+1, 0));
cnt_x.assign(H+1, vector<int>(W+1, 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';
}
