#include <bits/stdc++.h>
using namespace std;
const long long MAX = 3e5 + 9;
int main() {
  ios_base::sync_with_stdio(false);
  long long n, k;
  cin >> n >> k;
  string s[9];
  long long lol[9];
  for (int i = 0; i < k; i++) lol[i] = i;
  for (int i = 0; i < n; i++) cin >> s[i];
  long long ans = 100000000000;
  do {
    long long m1 = 0, m2 = 100000000000;
    for (int i = 0; i < n; i++) {
      long long c = 0;
      for (int j = 0; j < k; j++) c = c * 10 + s[i][lol[j]] - '0';
      m1 = max(m1, c);
      m2 = min(m2, c);
    }
    ans = min(ans, m1 - m2);
  } while (next_permutation(lol, lol + k));
  cout << ans;
  return 0;
}
