#include <bits/stdc++.h>
// clang-format off
using namespace std; using ll=long long; using ull=unsigned long long; using pll=pair<ll,ll>; const ll INF=4e18;
void print0(){}; template<typename H,typename... T> void print0(H h,T... t){cout<<h;print0(t...);}
void print(){print0("\n");}; template<typename H,typename... T>void print(H h,T... t){print0(h);if(sizeof...(T)>0)print0(" ");print(t...);}
void perr0(){}; template<typename H,typename... T> void perr0(H h,T... t){cerr<<h;perr0(t...);}
void perr(){perr0("\n");}; template<typename H,typename... T>void perr(H h,T... t){perr0(h);if(sizeof...(T)>0)perr0(" ");perr(t...);}
void ioinit() { cout<<fixed<<setprecision(15); cerr<<fixed<<setprecision(6); ios_base::sync_with_stdio(0); cin.tie(0); }
#define debug1(a) { cerr<<#a<<":"<<a<<endl; }
#define debug2(a,b) { cerr<<#a<<":"<<a<<" "<<#b<<":"<<b<<endl; }
#define debug3(a,b,c) { cerr<<#a<<":"<<a<<" "<<#b<<":"<<b<<" "<<#c<<":"<<c<<endl; }
#define debug4(a,b,c,d) { cerr<<#a<<":"<<a<<" "<<#b<<":"<<b<<" "<<#c<<":"<<c<<" "<<#d<<":"<<d<<endl; }
// clang-format on

// DPをにぶたん
// 遅延セグ木やlower_bound使っても大丈夫かな... 尺取りの方が無難ではある
ll N, M;
ll D[1505][1505];
bool accept(ll diff) {
    vector<bool> dp(M + 1, true);
    vector<bool> ndp(M + 1);
    for (ll i = 1; i < N; i++) {
        ll right = -1;
        for (ll j = 0; j < M; j++) {
            if (!dp[j]) continue;

            ll cur = D[i - 1][j];
            while (right + 1 < M && D[i][right + 1] < cur) {
                right++;
            }
            while (right + 1 < M && D[i][right + 1] <= cur + diff) {
                ndp[right + 1] = true;
                right++;
            }
        }
        swap(dp, ndp);
        for (ll j = 0; j < M; j++) {
            ndp[j] = false;
        }
    }
    for (ll j = 0; j < M; j++) {
        if (dp[j]) return true;
    }
    return false;
}
int main() {
    ioinit();
    cin >> N >> M;
    for (ll i = 0; i < N; i++) {
        vector<ll> DD;
        for (ll j = 0; j < M; j++) {
            ll d;
            cin >> d;
            DD.push_back(d);
        }
        sort(DD.begin(), DD.end());
        for (ll j = 0; j < M; j++) {
            D[i][j] = DD[j];
        }
    }
    if (N == 1) {
        print(0);
        return 0;
    }
    const ll MX = 1000000001;
    ll left = 0;
    ll right = MX - 1;
    ll ans = MX;
    while (left <= right) {
        ll mid = (left + right) / 2;
        if (accept(mid)) {
            ans = mid;
            right = mid - 1;
        } else {
            left = mid + 1;
        }
    }
    if (ans == MX) ans = -1;
    print(ans);
    return 0;
}