#include <bits/stdc++.h>
using namespace std;
const int maxn = 10;
const int INF = 2147000000;
int n, k;
int a[maxn][maxn];
int b[maxn], vis[maxn];
int ans = INF;
int make(int num) {
  int res = 0;
  for (int i = 1; i <= k; i++) {
    int c = b[i];
    res = res * 10 + a[num][c];
  }
  return res;
}
void solve() {
  int Max = -INF, Min = INF;
  for (int i = 1; i <= n; i++) {
    int res = make(i);
    Max = max(Max, res);
    Min = min(Min, res);
  }
  ans = min(ans, Max - Min);
}
void dfs(int cur) {
  if (cur == k + 1) {
    solve();
    return;
  }
  for (int i = 1; i <= k; i++) {
    if (!vis[i]) {
      vis[i] = 1;
      b[cur] = i;
      dfs(cur + 1);
      vis[i] = 0;
    }
  }
}
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= k; j++) {
      char c;
      scanf(" %c", &c);
      a[i][j] = c - '0';
    }
  }
  memset(vis, 0, sizeof(vis));
  dfs(1);
  printf("%d\n", ans);
  return 0;
}
