#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using str = string;
const char nl = '\n';
;
str to_string(char c) { return str(1, c); }
str to_string(bool b) { return b ? "true" : "false"; }
str to_string(const char* second) { return (str)second; }
str to_string(str second) { return second; }
template <class A>
str to_string(complex<A> c) {
  stringstream ss;
  ss << c;
  return ss.str();
}
str to_string(vector<bool> v) {
  str res = "{";
  for (int i = 0; i < v.size(); i++) res += char('0' + v[i]);
  res += "}";
  return res;
}
template <size_t SZ>
str to_string(bitset<SZ> b) {
  str res = "";
  for (int i = 0; i < b.size(); i++) res += char('0' + b[i]);
  return res;
}
template <class A, class B>
str to_string(pair<A, B> p);
template <class T>
str to_string(T v) {
  bool fst = 1;
  str res = "{";
  for (const auto& x : v) {
    if (!fst) res += ", ";
    fst = 0;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <class A, class B>
str to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
void DBG() { cerr << "]" << endl; }
template <class H, class... T>
void DBG(H h, T... t) {
  cerr << to_string(h);
  if (sizeof...(t)) cerr << ", ";
  DBG(t...);
}
int n, k;
vector<string> bruh(n);
vi perm;
int fin(vi& q, string second, int k) {
  int ret = 0, temp = 1;
  for (int i = 0; i < k; i++) {
    ret += temp * (second[q[i]]);
    temp *= 10;
  }
  return ret;
}
signed main() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cin >> n >> k;
  bruh.resize(n);
  for (int i = 0; i < k; i++) perm.push_back(i);
  for (int i = 0; i < n; i++) cin >> bruh[i];
  int ans = 1e9;
  do {
    int mi = 1e9, ma = -1e9;
    for (int i = 0; i < n; i++) {
      int bru = fin(perm, bruh[i], k);
      mi = min(mi, bru);
      ma = max(ma, bru);
    }
    ans = min(ans, ma - mi);
  } while (next_permutation(perm.begin(), perm.end()));
  cout << ans << nl;
}
