#include <bits/stdc++.h>
using namespace std;
int n, m, fi, co, x, y, nums[1000001];
char mat[1001][1001];
char a[1000001], b[1000001], c[1000001];
int la, lb, lc;
int primos[1000001], cntp;
bool mark[1000001];
int per[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
long long fact[10];
int main() {
  fact[1] = 1;
  for (int i = 2; i < 10; i++) fact[i] = fact[i - 1] * i;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    cin >> mat[i];
  }
  int resp = -1;
  for (int i = 0; i < fact[m]; i++) {
    for (int j = 0; j < n; j++) {
      nums[j] = 0;
      for (int k = 0; k < m; k++) {
        nums[j] = 10 * nums[j] + mat[j][per[k]] - '0';
      }
    }
    sort(nums, nums + n);
    if (resp == -1)
      resp = nums[n - 1] - nums[0];
    else
      resp = min(resp, nums[n - 1] - nums[0]);
    next_permutation(per, per + m);
  }
  cout << resp;
  return 0;
}
