#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
#include <iterator>
#include <string>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cmath>
#include <ctime>
#include <iomanip>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <random>
#include <utility>
#include <functional>
using namespace std;
void Main()
{
	int N,M;
	cin >> N >> M;
	vector<vector<int>> D(N,vector<int>(M));
	for(int i = 0;i < N;i++)
	{
		for(int j = 0;j < M;j++)
		{
			cin >> D[i][j];
		}
		sort(D[i].begin(),D[i].end());
	}
	int ng = -1,ok = (int)1e9;
	while(ok - ng > 1)
	{
		int mid = (ok + ng) / 2;
		vector<int> dp(M,1);
		for(int i = 1;i < N;i++)
		{
			for(int j = 1;j < M;j++)
			{
				dp[j] += dp[j - 1];
			}
			vector<int> n_dp(M);
			//D[i - 1][k] >= D[i][j] - mid && D[i - k] <= D[i][j]
			int l = 0,r = 0;
			for(int j = 0;j < M;j++)
			{
				while(r < M && D[i - 1][r] <= D[i][j])
				{
					r++;
				}
				while(l < M && D[i - 1][l] < D[i][j] - mid)
				{
					l++;
				}
				int cur = 0;
				if(r > 0)
				{
					cur += dp[r - 1];
				}
				if(l > 0)
				{
					cur -= dp[l - 1];
				}
				if(cur)
				{
					n_dp[j] = 1;
				}
			}
			swap(dp,n_dp);
		}
		bool check = false;
		for(int j = 0;j < M;j++)
		{
			check |= dp[j];
		}
		if(check)
		{
			ok = mid;
		}
		else
		{
			ng = mid;
		}
	}
	int ans = ok;
	if(ans == (int)1e9)
	{
		ans = -1;
	}
	cout << ans << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) Main();
}