#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <climits>
using namespace std;
int H, W;
vector<vector<int>> altitude;
const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};
// Check if a cell is within bounds
bool is_valid(int x, int y) {
return x >= 0 && x < H && y >= 0 && y < W;
}
// Flood-fill to check connectivity
void flood_fill(int x, int y, int min_alt, int max_alt, vector<vector<bool>> &visited) {
queue<pair<int, int>> q;
q.emplace(x, y);
visited[x][y] = true;
while (!q.empty()) {
auto [cx, cy] = q.front();
q.pop();
for (int d = 0; d < 4; ++d) {
int nx = cx + dx[d];
int ny = cy + dy[d];
if (is_valid(nx, ny) && !visited[nx][ny] &&
altitude[nx][ny] >= min_alt && altitude[nx][ny] <= max_alt) {
visited[nx][ny] = true;
q.emplace(nx, ny);
}
}
}
}
// Check if it's possible to divide the grid into 2 regions with max altitude difference <= T
bool can_divide(int T) {
int min_alt = INT_MAX, max_alt = INT_MIN;
// Determine global min/max altitude
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
min_alt = min(min_alt, altitude[i][j]);
max_alt = max(max_alt, altitude[i][j]);
}
}
for (int lower_bound = min_alt; lower_bound <= max_alt; ++lower_bound) {
int upper_bound = lower_bound + T;
if (upper_bound > max_alt) break;
vector<vector<bool>> visited(H, vector<bool>(W, false));
int regions_count = 0;
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
if (!visited[i][j] && altitude[i][j] >= lower_bound && altitude[i][j] <= upper_bound) {
++regions_count;
if (regions_count > 2) return false; // Early exit if more than 2 regions
flood_fill(i, j, lower_bound, upper_bound, visited);
}
}
}
if (regions_count == 2) return true; // Valid division found
}
return false; // No valid division found for this T
}
int main() {
cin >> H >> W;
altitude.resize(H, vector<int>(W));
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
cin >> altitude[i][j];
}
}
int left = 0, right = INT_MAX, result = INT_MAX;
while (left <= right) {
int mid = left + (right - left) / 2;
if (can_divide(mid)) {
result = mid;
right = mid - 1;
} else {
left = mid + 1;
}
}
cout << result << endl;
return 0;
}
