#define DEBUG 0
#include <bits/stdc++.h>
using namespace std;
#if DEBUG
// basic debugging macros
int __i__,__j__;
#define printLine(l) for(__i__=0;__i__<l;__i__++){cout<<"-";}cout<<endl
#define printLine2(l,c) for(__i__=0;__i__<l;__i__++){cout<<c;}cout<<endl
#define printVar(n) cout<<#n<<": "<<n<<endl
#define printArr(a,l) cout<<#a<<": ";for(__i__=0;__i__<l;__i__++){cout<<a[__i__]<<" ";}cout<<endl
#define print2dArr(a,r,c) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<a[__i__][__j__]<<" ";}cout<<endl;}
#define print2dArr2(a,r,c,l) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<setw(l)<<setfill(' ')<<a[__i__][__j__]<<" ";}cout<<endl;}
// advanced debugging class
// debug 1,2,'A',"test";
class _Debug {
public:
template<typename T>
_Debug& operator,(T val) {
cout << val << endl;
return *this;
}
};
#define debug _Debug(),
#else
#define printLine(l)
#define printLine2(l,c)
#define printVar(n)
#define printArr(a,l)
#define print2dArr(a,r,c)
#define print2dArr2(a,r,c,l)
#define debug
#endif
// define
#define MAX_VAL 999999999
#define MAX_VAL_2 999999999999999999LL
#define EPS 1e-6
#define mp make_pair
#define pb push_back
// typedef
typedef unsigned int UI;
typedef long long int LLI;
typedef unsigned long long int ULLI;
typedef unsigned short int US;
typedef pair<int,int> pii;
typedef pair<LLI,LLI> plli;
typedef vector<int> vi;
typedef vector<LLI> vlli;
typedef vector<pii> vpii;
typedef vector<plli> vplli;
// ---------- END OF TEMPLATE ----------
int A[2000][2000],A2[2000][2000];
int pre[2000][2000];
int query(int l,int r,int u,int d) {
return pre[d+1][r+1]-pre[u][r+1]-pre[d+1][l]+pre[u][l];
}
int main() {
int i,j;
int H,W;
scanf("%d %d",&H,&W);
for (i = 0; i < H; i++) {
for (j = 0; j < W; j++) scanf("%d",&A[i][j]);
}
int s = A[0][0],b = A[0][0];
for (i = 0; i < H; i++) {
for (j = 0; j < W; j++) s = min(s,A[i][j]),b = max(b,A[i][j]);
}
int l = 0,r = b-s;
while (l < r) {
int m = (l+r) / 2;
for (i = 0; i < H; i++) {
for (j = 0; j < W; j++) {
if (A[i][j]-s > m) pre[i+1][j+1] = 1;
else pre[i+1][j+1] = 0;
}
}
for (i = 1; i <= H; i++) {
for (j = 1; j <= W; j++) pre[i][j] += pre[i-1][j]+pre[i][j-1]-pre[i-1][j-1];
}
int f[4];
f[0] = f[1] = f[2] = f[3] = 0;
for (i = 0; i < H; i++) {
for (j = 0; j < W; j++) {
if (b-A[i][j] > m) {
if (query(0,j,0,i) > 0) f[0] = 1;
if (query(j,W-1,0,i) > 0) f[1] = 1;
if (query(0,j,i,H-1) > 0) f[2] = 1;
if (query(j,W-1,i,H-1) > 0) f[3] = 1;
}
}
}
if (!f[0] || !f[1] || !f[2] || !f[3]) r = m;
else l = m+1;
}
printf("%d\n",l);
return 0;
}
