import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
sys.setrecursionlimit(1000000)
import math
import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
from collections import defaultdict
from collections import deque
#import copy #DeepCopy: hoge = [_[:] for _ in hogehoge]
#from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]

class SegmentTree(object):
    def __init__(self, A, dot, unit):
        n = 1 << (len(A) - 1).bit_length()
        tree = [unit] * (2 * n)
        for i, v in enumerate(A):
            tree[i + n] = v
        for i in range(n - 1, 0, -1):
            tree[i] = dot(tree[i << 1], tree[i << 1 | 1])
        self._n = n
        self._tree = tree
        self._dot = dot
        self._unit = unit

    def __getitem__(self, i):
        return self._tree[i + self._n]

    def update(self, i, v):
        i += self._n
        self._tree[i] = v
        while i != 1:
            i >>= 1
            self._tree[i] = self._dot(self._tree[i << 1], self._tree[i << 1 | 1])

    def add(self, i, v):
        self.update(i, self[i] + v)

    def sum(self, l, r): #これで[l,r)から取り出す。
        l += self._n
        r += self._n
        l_val = r_val = self._unit
        while l < r:
            if l & 1:
                l_val = self._dot(l_val, self._tree[l])
                l += 1
            if r & 1:
                r -= 1
                r_val = self._dot(self._tree[r], r_val)
            l >>= 1
            r >>= 1
        return self._dot(l_val, r_val)


def main():
    N,M = map(int,input().split()); INF = 1<<60
    D = [list(map(int,input().split())) for _ in range(N)]
    for i in range(N):
        D[i].sort()

    def check(x):
        Tree = SegmentTree([x]*M,min,INF)
        for i in range(1,N):
            # output
            # output = [Tree[j] for j in range(M)]
            # print("output",output)
            NTree = SegmentTree([INF]*M,min,INF)
            preDi = [-INF] + D[i-1]
            # print(preDi)
            left = 0; right = 0
            for j in range(M):
                # left = bisect.bisect_left(preDi,D[i][j] - x)
                # right = bisect.bisect_right(preDi,D[i][j])
                while left < M+1 and preDi[left] < D[i][j] - x:
                    left += 1
                while right < M+1 and preDi[right] <= D[i][j]:
                    right += 1
                val = Tree.sum(left-1, right-1)
                # print(left,right,val)
                if val <= x:
                    NTree.update(j,x)
            NTree,Tree = Tree,NTree
        # output = [Tree[j] for j in range(M)]
        # print("output",output)
        # print("handan",Tree.sum(0,M))
        if Tree.sum(0,M) <= x:
            return True
        else:
            return False



    ok = pow(10,9)
    ng = -1
    while abs(ok-ng) > 1:
        mid = (ok+ng)//2
        if check(mid):
            ok = mid
        else:
            ng = mid
    if ok == pow(10,9):
        print(-1)
    else:
        print(ok)







if __name__ == '__main__':
    main()