#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	vector<vector<int>> a(n, vector<int>(m));
	rep(i, n) {
		rep(j, m) cin >> a[i][j];
		sort(all(a[i]));
	}
	long long ng = -1;
	long long ok = INF + 1;
	while (1 < abs(ok - ng)) {
		long long mid = (ng + ok) / 2;
		auto check = [&]() {
			vector<vector<bool>> dp(n, vector<bool>(m));
			rep(i, m)dp[0][i] = 1;
			rep(i, n - 1) {
				int k = 0;
				rep(j, m) {
					if (!dp[i][j])continue;
					int l = a[i][j];
					int r = a[i][j] + mid;
					while ((k < m) && (a[i + 1][k] < l)) {
						k++;
					}
					while ((k < m) && (a[i + 1][k] <= r)) {
						dp[i + 1][k] = true;
						k++;
					}
				}
			}
			rep(i, m)if (dp[n - 1][i])return true;
			return false;
		};
		if (check()) ok = mid;
		else ng = mid;
	}
	if (ok == INF + 1)cout << -1 << endl;
	else cout << ok << endl;

	return 0;
}