#include <bits/stdc++.h>
using namespace std;
const double PI = 3.14159265358979323846;
const double eps = (1e-8);
int n, k;
string s[10];
int ans;
vector<int> a;
int findAns() {
  int mx = INT_MIN, mn = INT_MAX;
  for (int i = 0; i < n; ++i) {
    int temp = 0;
    for (int j = 0; j < k; ++j) {
      temp = temp * 10 + s[i][a[j]] - '0';
    }
    mx = max(mx, temp);
    mn = min(mn, temp);
  }
  return mx - mn;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> k;
  for (int i = 0; i < n; ++i) cin >> s[i];
  ans = INT_MAX;
  for (int i = 0; i < k; ++i) a.push_back(i);
  do {
    ans = min(ans, findAns());
  } while (next_permutation(a.begin(), a.end()));
  cout << ans;
  return 0;
}
