#include <bits/stdc++.h>
using namespace std;
long long n, k, l, x, ans(1e18), b[10], a[10][10];
bitset<10> visit;
vector<long long> v;
void cari(long long x) {
  if (x == k + 1) {
    for (int i = 0; i < n; i++) {
      long long tmp = 0;
      for (int j = 0; j < v.size(); j++) {
        tmp *= 10;
        tmp += a[i][v[j]];
      }
      b[i] = tmp;
    }
    sort(b, b + n);
    ans = min(ans, b[n - 1] - b[0]);
  } else {
    for (int i = 1; i <= k; i++) {
      if (!visit[i]) {
        visit[i] = true;
        v.push_back(i);
        cari(x + 1);
        visit[i] = false;
        v.pop_back();
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    cin >> x;
    l = k;
    while (x) {
      a[i][l] = x % 10;
      x /= 10;
      l--;
    }
  }
  cari(1);
  cout << ans << '\n';
  return 0;
}
