#include <bits/stdc++.h>
using namespace std;
const long long MXN = 1e5 + 10;
const long long M = 1e9 + 7;
long long n, k;
string str[10], tmp[10];
long long calc(long long ind) {
  long long res = 0;
  for (long long i = 0; i < k; ++i) {
    res *= 10;
    res += tmp[ind][i] - '0';
  }
  return res;
}
int32_t main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cin >> n >> k;
  vector<long long> p(k);
  for (long long i = 0; i < k; ++i) p[i] = i;
  long long ans = 1e10;
  for (long long i = 0; i < n; ++i) cin >> str[i];
  do {
    for (long long i = 0; i < n; ++i) {
      for (long long j = 0; j < k; ++j) {
        tmp[i][j] = str[i][p[j]];
      }
    }
    vector<long long> v;
    for (long long i = 0; i < n; ++i) {
      v.push_back(calc(i));
    }
    sort(v.begin(), v.end());
    ans = min(ans, v[n - 1] - v[0]);
  } while (next_permutation(p.begin(), p.end()));
  cout << ans << '\n';
  return 0;
}
