#include <bits/stdc++.h>
using namespace std;
int main() {
  string s[10];
  int a[10];
  long long n, k, c = 0, d = 1, max1 = -100000, min1 = 999999999,
                  ans = 999999999;
  cin >> n >> k;
  for (int i = 0; i <= 10; i++) a[i] = i;
  for (int i = 0; i < n; i++) cin >> s[i];
  if (k == 1) {
    for (int i = 0; i < n; i++) {
      if (s[i][0] - 48 > max1) max1 = s[i][0] - 48;
      if (s[i][0] - 48 < min1) min1 = s[i][0] - 48;
    }
    ans = max1 - min1;
  }
  for (int i = 0; i < n; i++) {
    for (int j = k - 1; j >= 0; j--) {
      c += (s[i][a[j]] - 48) * d;
      d *= 10;
    }
    if (c > max1) max1 = c;
    if (c < min1) min1 = c;
    c = 0;
    d = 1;
  }
  ans = max1 - min1;
  max1 = 0;
  min1 = 999999999;
  while (next_permutation(a, a + k)) {
    for (int i = 0; i < n; i++) {
      for (int j = k - 1; j >= 0; j--) {
        c += (s[i][a[j]] - 48) * d;
        d *= 10;
      }
      if (c > max1) max1 = c;
      if (c < min1) min1 = c;
      c = 0;
      d = 1;
    }
    if (max1 - min1 < ans) ans = max1 - min1;
    max1 = 0;
    min1 = 999999999;
  }
  cout << ans << endl;
  return 0;
}
