#include <bits/stdc++.h>
using namespace std;
const long long int MOD = 1000000007;
const long double PI = 2 * acos(0.0);
const vector<long long int> dx = {1, -1, 0, 0};
const vector<long long int> dy = {0, 0, 1, -1};
template <typename T = long long int>
vector<T> ga(long long int n, bool oneIndexed = false) {
  vector<T> a = vector<T>(n + oneIndexed);
  for (long long int i = 0; i < n; i++) {
    T p;
    cin >> p;
    a[i + oneIndexed] = p;
  }
  return move(a);
}
template <typename T, typename A>
void pa(vector<T, A> const &a, long long int begin = 0,
        long long int end = -1) {
  if (end == -1) end = (long long int)a.size() - 1;
  for (long long int i = begin; i <= end; i++) {
    cout << a[i] << " ";
  }
  cout << "\n";
}
template <typename T, typename A>
void papair(vector<T, A> const &a, long long int begin = 0,
            long long int end = -1) {
  if (end == -1) end = (long long int)a.size() - 1;
  for (long long int i = begin; i <= end; i++) {
    cout << a[i].first << " " << a[i].second << "\n";
  }
}
void solve() {
  long long int n;
  cin >> n;
  long long int k;
  cin >> k;
  vector<string> nums(n);
  for (long long int i = 0; i < n; i++) {
    cin >> nums[i];
  }
  vector<long long int> cur_perm;
  for (long long int i = 0; i < k; i++) {
    cur_perm.push_back(i);
  }
  long long int ans = 1e18;
  do {
    long long int mi = 1e18;
    long long int ma = 0;
    for (long long int i = 0; i < n; i++) {
      long long int cn = 0;
      for (long long int j = 0; j < k; j++) {
        cn = 10 * cn + (char)(nums[i][cur_perm[j]] - '0');
      }
      if (cn < mi) mi = cn;
      ;
      if (cn > ma) ma = cn;
      ;
    }
    if ((ma - mi) < ans) ans = (ma - mi);
    ;
  } while (next_permutation(cur_perm.begin(), cur_perm.end()));
  cout << ans << '\n';
}
int main(void) {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
