#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
int inf = 2e9;
void solve(){
int n, m;
cin >> n >> m;
vector<vector<int>> a(n, vector<int> (m));
array<int,3> mx = {0, 0, 0}, mn = {inf, 0, 0};
for(int i = 0; i < n; i ++ )
for(int j = 0; j < m; j ++ ){
cin >> a[i][j];
if(mx[0] <= a[i][j]) mx = {a[i][j], i, j};
if(mn[0] >= a[i][j]) mn = {a[i][j], i, j};
}
int l = 0, r = mx[0] - mn[0], ans = r;
vector<int> dx = {-1,1,0,0}, dy = {0,0,-1,1};
auto ok = [&](int i, int j) -> bool {
return (i >= 0 && i < n && j >= 0 && j < m);
};
auto ch = [&]( int mid ) -> bool {
//cout << mid << endl;
vector<vector<int>> us1(n, vector<int> (m, 0));
vector<vector<int>> us2(n, vector<int> (m, 0));
queue<array<int,2>> q;
q.push({mn[1], mn[2]});
us1[mn[1]][mn[2]] = 1;
while(q.size()){
auto [i, j] = q.front();
q.pop();
//cout << i << ' ' << j << '\n';
for(int k = 0; k < 4; k ++ ){
int ni = i + dx[k], nj = j + dy[k];
if(ok(ni, nj) && !us1[ni][nj] && a[ni][nj] - mn[0] <= mid){
us1[ni][nj] = 1;
q.push({ni, nj});
}
}
};
//cout << '\n';
q.push({mx[1], mx[2]});
us2[mx[1]][mx[2]] = 1;
while(q.size()){
auto [i, j] = q.front();
q.pop();
//cout << i << ' ' << j << '\n';
for(int k = 0; k < 4; k ++ ){
int ni = i + dx[k], nj = j + dy[k];
if(ok(ni, nj) && !us2[ni][nj] && mx[0] - a[ni][nj] <= mid){
us2[ni][nj] = 1;
q.push({ni, nj});
}
}
};
//cout << '\n';
for(int i = 0; i < n; i ++ )
for(int j = 0; j < m; j ++ )
if(!(us1[i][j] || us2[i][j]))return 0;
return 1;
};
while( l <= r ) {
int m = (l + r) >> 1;
if(ch(m)){
ans = m;
r = m - 1;
}else l = m + 1;
};
cout << ans << '\n';
};
signed main(){
ios_base::sync_with_stdio();
cin.tie(nullptr); cout.tie(nullptr);
int tt = 1;
//cin >> tt;
while(tt -- ){
solve();
};
};
