/** * author: shu8Cream * created: 01.01.2023 15:33:24 **/ #include using namespace std; #define overload3(a,b,c,d,...) d #define rep1(i,n) for (int i=0; i<(n); i++) #define rep2(i,a,n) for (int i=(a); i<(n); i++) #define rep(...) overload3(__VA_ARGS__, rep2, rep1)(__VA_ARGS__) #define rrep1(i,n) for (int i=(n-1); i>=0; i--) #define rrep2(i,a,n) for (int i=(n-1); i>=(a); i--) #define rrep(...) overload3(__VA_ARGS__, rrep2, rrep1)(__VA_ARGS__) #define all(x) (x).begin(), (x).end() #define rall(x) (x).rbegin(), (x).rend() #define sz(x) int((x).size()) #define pcnt __builtin_popcountll using ll = long long; using P = pair; template using vc = vector; template using vv = vc>; using vi = vc; using vvi = vv; const int INF = 1e9; const ll LINF = 8e18; templateistream& operator>>(istream&i,vc&v){rep(j,sz(v))i>>v[j];return i;} templatestring join(const T&v,const string& d=""){stringstream s;rep(i,sz(v))(i?s<ostream& operator<<(ostream&o,const vc&v){if(sz(v))o<istream& operator>>(istream&i,pair&v){return i>>v.first>>v.second;} templateostream& operator<<(ostream&o,const pair&v){return o< inline bool chmax(T& a, T b) {if(a inline bool chmin(T& a, T b) {if(a>b) { a=b;return true; } return false;} template string to_string(T s); template string to_string(pair p); string to_string(char c) { return string(1, c); } string to_string(string s) { return s; } string to_string(const char s[]) { return string(s); } template string to_string(T v) { if (v.empty()) return "{}"; string ret = "{"; for (auto x : v) ret += to_string(x) + ","; ret.back() = '}'; return ret; } template string to_string(pair p) { return "{" + to_string(p.first) + ":" + to_string(p.second) + "}"; } void debug_out() { cout << endl; } template void debug_out(Head H, Tail... T) { cout << to_string(H) << " "; debug_out(T...); } #ifdef _DEBUG #define debug(...) debug_out(__VA_ARGS__) #else #define debug(...) #endif int main() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); ll n,m; cin >> n >> m; vvi d(n,vi(m)); rep(i,n){ cin >> d[i]; sort(all(d[i])); } set

cand; rep(i,m)rep(j,m){ if(d[0][i]>d[n-1][j]) continue; cand.emplace(d[0][i],d[n-1][j]); } ll ans = LINF; for(auto[l,r]:cand){ ll now = l; rep(i,1,n-1){ int it = lower_bound(all(d[i]),now) - d[i].begin(); if(it==m){ now = r+1; break; } now = d[i][it]; } if(now<=r) chmin(ans,r-l); } if(ans==LINF) ans=-1; cout << ans << endl; }