#include <bits/stdc++.h>

#define endl '\n'
#define left jhghajkhja
#define right oauighgajk
#define prev aioghajga
#define next ioyhjhfajasj
#define y0 iuadoghasdgj
#define y1 taklahgjkla
#define remainder pogjuakllhga
#define pow pajklgaklha
#define pow10 iopuioadjlgkah
#define div aljghajkghak
#define distance gkuftgjasgfjh
#define uppercase ifyhasjkhakjfas
#define count sajhfkajfa
#define rank asfhujfasj

//#define floor hjakjhaja
//#define time ashjlahjka
//#define double_t double
//#define tm kahjflahaajk

using namespace std;

const int N = 1024;
const int INF = (1e9) + 7;

int n,m,a[N][N],arr[N*N],sz,ptr[N],ans;
struct cmp {
	bool operator ()(const int &x, const int &y) const {
		return a[x][ptr[x]]>a[y][ptr[y]];
	}
};
priority_queue < int, vector < int >, cmp > q;
int curr,max_value;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	//freopen("test.txt","r",stdin);
	//freopen(IN.c_str(),"r",stdin);
	//freopen(OUT.c_str(),"w",stdout);
	int i,j;
	
	scanf("%d %d", &n, &m);
	for(i=1;i<=n;i++) {
		for(j=1;j<=m;j++) {
			scanf("%d", &a[i][j]);
			arr[++sz]=a[i][j];
		}
		ptr[i]=1;
		sort(a[i]+1,a[i]+1+m);
		a[i][m+1]=INF;
		q.push(i);
		max_value=max(max_value,a[i][ptr[i]]);
	}
	sort(arr+1,arr+1+sz);
	ans=INF;
	for(i=1;i<=sz;i++) {
		if(max_value>arr[i]) continue;
		while(true) {
			curr=q.top();
			if(a[curr][ptr[curr]+1]>arr[i]) break;
			q.pop();
			++ptr[curr];
			max_value=max(max_value,a[curr][ptr[curr]]);
			q.push(curr);
		}
		ans=min(ans,arr[i]-a[q.top()][ptr[q.top()]]);
	}
	printf("%d\n", ans);
	
	//fprintf(stderr, "Time: %d ms\n", (int)(clock()*1000.0/CLOCKS_PER_SEC));
	
	return 0;
}