#define _USE_MATH_DEFINES #include using namespace std; #define FOR(i,m,n) for(int i=(m);i<(n);++i) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() using ll = long long; constexpr int INF = 0x3f3f3f3f; constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL; constexpr double EPS = 1e-8; constexpr int MOD = 998244353; // constexpr int MOD = 1000000007; constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1}; constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1}; constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1}; template inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; } template inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; } struct IOSetup { IOSetup() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << fixed << setprecision(20); } } iosetup; int main() { constexpr int D = 1000000000; int n, m; cin >> n >> m; vector d(n, vector(m, 0)); REP(i, n) { REP(j, m) cin >> d[i][j]; sort(ALL(d[i])); } int lb = -1, ub = D; while (ub - lb > 1) { const int f = (lb + ub) / 2; vector dp(m, true), nxt(m); FOR(i, 1, n) { fill(ALL(nxt), false); int l = 0, r = 0, num = 0; REP(j, m) { for (; r < m && d[i - 1][r] <= d[i][j]; ++r) num += dp[j]; for (; l < r && d[i - 1][l] + f < d[i][j]; ++l) num -= dp[j]; if (num > 0) nxt[j] = true; } dp.swap(nxt); } (count(ALL(dp), true) > 0 ? ub : lb) = f; } cout << (ub == D ? -1 : ub) << '\n'; return 0; }