#include <bits/stdc++.h>
using namespace std;
const long long int Mod = 998244353;
const long long int mod = 1e9 + 7;
long long int Pow(long long int a, long long int b) {
  a = a % mod;
  long long int res = 1;
  while (b) {
    if (b & 1) res = (res * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return (res % mod);
}
long long int modInverse(long long int a, long long int m) {
  long long int m0 = m;
  long long int y = 0, x = 1;
  if (m == 1) return 0;
  while (a > 1) {
    long long int q = a / m;
    long long int t = m;
    m = a % m, a = t;
    t = y;
    y = x - q * y;
    x = t;
  }
  if (x < 0) x += m0;
  return x;
}
void solve() {
  int n, k;
  cin >> n >> k;
  int arr[n][k];
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < k; j++) {
      char ch;
      cin >> ch;
      arr[i][j] = (ch - '0');
    }
  }
  int per[k];
  for (int i = 0; i < k; i++) {
    per[i] = i;
  }
  int ans = 1e9;
  do {
    int mi = 1e9;
    int ma = -1e9;
    for (int i = 0; i < n; i++) {
      int val = 0;
      for (int j = 0; j < k; j++) {
        (val *= 10) += arr[i][per[j]];
      }
      ma = max(ma, val);
      mi = min(mi, val);
    }
    ans = min(ans, ma - mi);
  } while (next_permutation(per, per + k));
  cout << ans;
}
int main() {
  solve();
  return 0;
}
