#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000;
const int MAX = 1000;
const int inf = 999999999;
const int p1 = 104393321, p2 = 104393329;
int a[MAX], d[MAX][MAX];
int main() {
  ios::sync_with_stdio(0);
  int n, k;
  cin >> n >> k;
  for (int i = (0); i < int(n); ++i) {
    cin >> a[i];
  }
  for (int i = (0); i < int(n); ++i) {
    int x = a[i];
    for (int j = (0); j < int(k); ++j) {
      d[i][j] = x % 10;
      x /= 10;
    }
  }
  int perm[MAX];
  for (int i = (0); i < int(k); ++i) perm[i] = i;
  int ans = inf;
  do {
    int t[MAX];
    fill(t, t + n, 0);
    for (int i = (0); i < int(n); ++i) {
      for (int j = (0); j < int(k); ++j) {
        t[i] *= 10;
        t[i] += d[i][perm[j]];
      }
    }
    sort(t, t + n);
    ans = min(ans, t[n - 1] - t[0]);
  } while (next_permutation(perm, perm + k));
  cout << ans << endl;
  return 0;
}
