#pragma GCC optimize("O3")
#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")	
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping") 
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,fma") 
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native") 
//#pragma GCC optimization ("unroll-loops")

#include <bits/stdc++.h>

using namespace std;

int n,m;
vector <vector<long long int>> v;
bool check[1500][1500];
int arr[1505];

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin >> n >> m;

	for(int i=0;i<n;i++)
	{
		vector <long long int> temp;
		for(int j=0;j<m;j++)
		{
			long long int t;
			cin >> t;
			temp.push_back(t);
		}
		sort(temp.begin(),temp.end());
		v.push_back(temp);
	}

	long long int res = 2e18;

	long long int lo = 0;
	long long int hi = 2e9;

	while(lo<=hi)
	{
		long long int mid = (lo + hi)/2;
		memset(check,false,sizeof(check));
		for(int i=0;i<m;i++)
		{
			check[0][i] = true;
		}

		for(int i=0;i<n-1;i++)
		{
			memset(arr,0,sizeof(arr));
			for(int j=0;j<m;j++)
			{
				if(check[i][j]==false) continue;
				long long int l = v[i][j];
				long long int r = v[i][j] + mid;
				int L = lower_bound(v[i+1].begin(),v[i+1].end(),l) - v[i+1].begin();
				int R = upper_bound(v[i+1].begin(),v[i+1].end(),r) - v[i+1].begin();
				if(L==m || R==0) continue;
				R-=1;
				if(v[i+1][R] - v[i][j] > mid) continue;
				if(v[i+1][L] - v[i][j] > mid) continue;
				if(L<=R)
				{
					arr[L] += 1;
					arr[R+1] -= 1;
				}
			}
			int val = 0;
			for(int j=0;j<m;j++)
			{
				val += arr[j];
				if(val > 0) check[i+1][j] = true;
			}
		}

		bool ok = false;
		for(int j=0;j<m;j++)
		{
			if(check[n-1][j])
			{
				ok = true;
				break;
			}
		}

		if(ok)
		{
			res = min(res,mid);
			hi = mid - 1;
		}
		else
		{
			lo = mid +1;
		}
	}

	if(res >= 2e18) res = -1;

	cout << res << '\n';
	
	return 0;
}