#include //#include using namespace std; //using namespace atcoder; //using mint = modint1000000007; //const int mod = 1000000007; //using mint = modint998244353; //const int mod = 998244353; const int INF = 1e9; //const long long LINF = 1e18; #define rep(i, n) for (int i = 0; i < (n); ++i) #define rep2(i,l,r)for(int i=(l);i<(r);++i) #define rrep(i, n) for (int i = (n-1); i >= 0; --i) #define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i) #define all(x) (x).begin(),(x).end() #define allR(x) (x).rbegin(),(x).rend() #define endl "\n" #define P pair template inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; } template inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; } int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int n, m; cin >> n >> m; vector> a(n, vector(m)); rep(i, n) { rep(j, m) cin >> a[i][j]; sort(all(a[i])); } long long ng = -1; long long ok = INF + 1; while (1 < abs(ok - ng)) { long long mid = (ng + ok) / 2; auto check = [&]() { vector> dp(n, vector(m)); rep(i, m)dp[0][i] = 1; rep(i, n - 1) { int k = 0; rep(j, m) { if (!dp[i][j])continue; int l = a[i][j]; int r = a[i][j] + mid; while ((k < m) && (a[i + 1][k] < l)) { k++; } while ((k < m) && (a[i + 1][k] <= r)) { dp[i + 1][k] = true; k++; } } } rep(i, m)if (dp[n - 1][i])return true; return false; }; if (check()) ok = mid; else ng = mid; } if (ok == INF + 1)cout << -1 << endl; else cout << ok << endl; return 0; }