#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
vector<int> alts;
vector<bool> arr;
int w,h;
bool valid(int lb, int ub, bool dx, bool dy) {
for (int y = 0; y < h; y++) {
for (int x = 0; x < w; x++) {
// if (alts[x+y*w] > lb && alts[x+y*w] < ub) return false;
arr[x+y*w] = (alts[x+y*w] > ub);
}
}
for (int y = dy?h-1:0; y < h && y >= 0; y += dy?-1:1) {
for (int x = dx?w-1:0; x < w && x >= 0; x += dx?-1:1) {
bool tmp = arr[x+y*w];
if (dx?x<w-1:x>0) tmp = tmp || arr[x+(dx?1:-1)+y*w];
if (dy?y<h-1:y>0) tmp = tmp || arr[x+(y+(dy?1:-1))*w];
if (tmp && alts[x+y*w] < lb) return false;
arr[x+y*w] = tmp;
}
}
return true;
}
int main() {
cin >> h >> w;
int la = 2000000000, ha = 0;
for (int y = 0; y < h; y++) {
for (int x = 0; x < w; x++) {
int tmp;
cin >> tmp;
alts.push_back(tmp);
la = min(la, tmp);
ha = max(ha, tmp);
}
}
arr.resize(w*h);
int l = 0, h = ha-la;
while (l+1<h) {
int m = (l+h)/2;
bool b = valid(ha-m, la+m, false, false) || valid(ha-m, la+m, true, false) || valid(ha-m, la+m, false, true) || valid(ha-m, la+m, true, true);
if (b) {
h = m;
} else {
l = m;
}
}
cout << h << "\n";
}
