#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-10;
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  int d[8][8];
  for (int i = 0; i < n; ++i) {
    char buf[32];
    scanf("%s", buf);
    for (int j = 0; j < k; ++j) d[i][j] = buf[j] - '0';
  }
  int permu[8] = {0, 1, 2, 3, 4, 5, 6, 7};
  int res = 1000000000;
  do {
    int c[8][8];
    for (int i = 0; i < n; ++i)
      for (int j = 0; j < k; ++j) c[i][permu[j]] = d[i][j];
    int nums[8], maxi, mini;
    maxi = 0;
    mini = 1000000000;
    for (int i = 0; i < n; ++i) {
      nums[i] = 0;
      for (int j = 0; j < k; ++j) nums[i] = nums[i] * 10 + c[i][j];
      maxi = max(maxi, nums[i]);
      mini = min(mini, nums[i]);
    }
    res = min(res, maxi - mini);
  } while (next_permutation(permu, permu + k));
  printf("%d\n", res);
  return 0;
}
