#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,s,a[1002][1002],l[1002],r[1002],ans=INT_MAX;
int main(){
    cin>>n>>s;
    for(ll i=1;i<=n;i++){
        for(ll j=1;j<=s;j++){
            cin>>a[i][j];
        }
        sort(a[i]+1,a[i]+s+1);
    }
    for(ll i=1;i<=s;i++){
        ll mid = a[1][i];
        vector<pair<ll,ll> > ls;
        for(ll j=2;j<=n;j++){
            l[j] = *lower_bound(a[j],a[j]+s+1,mid);
            if(l[j]==0) l[j] = INT_MAX;
            auto pr = upper_bound(a[j]+1,a[j]+s+1,mid);
            if(pr!=a[j]+1){
                pr--;
                r[j] = *pr;
            }
            else{
                r[j] = -INT_MAX;
            }
            // cout<<l[j]<<' '<<r[j]<<endl;
            ls.push_back({l[j],j});
        }
        sort(ls.begin(),ls.end());
        ans = min(ans,ls[ls.size()-1].first-mid);
        for(ll i=(int)ls.size()-1;i>0;i--){
            mid=min(mid,r[ls[i].second]);
            ans = min(ans,ls[i-1].first-mid);
            // cout<<ls[i].first<<' '<<mid<<' '<<ls[i].first-mid<<endl;
        }
        mid=min(mid,r[ls[0].second]);
        ans = min(ans,a[1][i]-mid);
        // cout<<ans<<endl;
    }
    cout<<ans<<endl;
}