#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, s;
    cin >> n >> s;
    vector<pair<int, int>> students;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < s; ++j) {
            int h;
            cin >> h;
            students.emplace_back(h, i);
        }
    }
    ranges::sort(students);
    
    vector<int> cnt(n);
    int r = 0, zero_cnt = n, ans = 1e9;
    for (int l = 0; l < n * s; ++l) {
        while (r < n * s && zero_cnt) {
            if (cnt[students[r].second]++ == 0) {
                --zero_cnt;
            }
            ++r;
        }
        if (zero_cnt == 0) {
            ans = min(ans, students[r - 1].first - students[l].first);
        }
        if (--cnt[students[l].second] == 0) {
            ++zero_cnt;
        }
    }
    cout << ans << '\n';
    return 0;
}