#include <bits/stdc++.h>
using namespace std;
int a[101], c[101];
char b[10][10];
char d[101][10];
int main() {
  int n, k;
  while (scanf("%d %d", &n, &k) != EOF) {
    for (int i = 1; i <= n; i++) scanf("%s", b[i]);
    for (int i = 1; i <= k; i++) c[i] = i;
    int ans = 1000000000;
    do {
      for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= k; j++) d[i][c[j] - 1] = b[i][j - 1];
      }
      int max_ = 0;
      int min_ = 1000000000;
      for (int i = 1; i <= n; i++) {
        int x = 0;
        for (int j = 0; j < k; j++) x = x * 10 + d[i][j] - '0';
        max_ = max(x, max_);
        min_ = min(x, min_);
      }
      ans = min(ans, max_ - min_);
    } while (next_permutation(c + 1, c + 1 + k));
    printf("%d\n", ans);
  }
}
