#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;

#include <bits/stdc++.h>
using namespace std;

int dp[1515][1515];
const int INF=1e9+7;

int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);

  for(int i=1;i<1515;i++) rep(j,1515) dp[i][j]=INF;
  
  int n,m;
  cin>>n>>m;
  vector<vector<int>> D(n,vector<int> (m));
  rep(i,n) rep(j,m) cin>>D[i][j];
  rep(i,n) sort(ALL(D[i]));
  
  for(int i=1;i<n;i++){
    for(int j=0;j<m;j++){
      auto r=upper_bound(ALL(D[i-1]),D[i][j])-D[i-1].begin();
      if(r==0) continue;
      int ok=r-1,ng=-1;
      while(ok-ng>1){
        int mid=(ok+ng)/2;
        if(dp[i-1][mid]-abs(D[i][j]-D[i-1][mid])>=0) ok=mid;
        else ng=mid;
      }
      if(ok>0) dp[i][j]=min(max(dp[i-1][ok],D[i][j]-D[i-1][ok]),max(dp[i-1][ok-1],D[i][j]-D[i-1][ok-1]));
      else if(ok==0) dp[i][j]=max(dp[i-1][ok],D[i][j]-D[i-1][ok]);
      else continue;
    }
  }
  int ans=INF;
  rep(j,m) ans=min(ans,dp[n-1][j]);
  if(ans==INF) cout<<-1<<endl;
  else cout<<ans<<endl;
  
  return 0;
}