#include <bits/stdc++.h>
using namespace std;
unsigned long long mod = 1000000007;
unsigned long long po(unsigned long long a, unsigned long long b) {
  unsigned long long ans = 1ll;
  while (b) {
    if (b & 1ll) {
      ans = (ans * a) % mod;
    }
    b = b >> 1ll;
    a = (a * a) % mod;
  }
  return (ans % mod);
}
int str_to_int(string t) {
  int num = 0;
  for (int j = 0; j < t.size(); j++) {
    num = num * 10 + (t[j] - '0');
  }
  return num;
}
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  char c = '1';
  string s = "";
  string S;
  int K = n;
  vector<int> initia;
  while (k--) {
    s = s + c;
    int x = c - '0';
    x++;
    c = x + '0';
  }
  vector<string> V;
  while (n--) {
    cin >> S;
    V.push_back(S);
    initia.push_back(str_to_int(S));
  }
  sort(initia.begin(), initia.end());
  int mn = initia[K - 1] - initia[0];
  while (next_permutation(s.begin(), s.end())) {
    vector<int> v;
    for (int i = 0; i < V.size(); i++) {
      string p = V[i];
      string nw = "";
      for (int l = 0; l < s.size(); l++) {
        char ch = p[(s[l] - '0') - 1];
        nw = nw + ch;
      }
      v.push_back(str_to_int(nw));
    }
    sort(v.begin(), v.end());
    int diff = v[K - 1] - v[0];
    if (mn > diff) mn = diff;
  }
  printf("%d\n", mn);
}
