from bisect import bisect_left, bisect_right
from itertools import accumulate


def find_interval(a: list, lo: int, hi: int) -> tuple[int, int, int]:
    """
    ソート済みリスト a の要素の lo 以上 hi 以下の個数と区間を返す
    return: 範囲内の個数, l, r
    """
    assert lo <= hi
    empty = 0, -1, -1  # 区間なし
    if not a or lo > a[-1] or hi < a[0]: return empty

    l = bisect_left(a, lo)
    r = bisect_right(a, hi) - 1
    if l > r: return empty
    return r-l+1, l, r


INF = 1 << 60
N, M = map(int, input().split())
D = []
for _ in range(N):
    D.append(sorted(map(int, input().split())))


# 距離 d 以下にできるか
def can(m):
    xs = [1] * (M+1)
    for i in range(1, N):
        ys = [0] * (M+1)
        for j in range(M):
            if xs[j] == 0: continue
            k = D[i-1][j]

            cnt, l, r = find_interval(D[i], k, k+m)
            if cnt > 0:
                ys[l] += 1
                ys[r+1] -= 1

        xs = list(accumulate(ys))

    return any(xs)


lo = 0
hi = 10**9
ans = hi
while lo <= hi:
    m = (lo + hi) // 2
    if can(m):
        ans = min(ans, m)
        hi = m - 1
    else:
        lo = m + 1

if ans == 10**9:
    print(-1)
else:
    print(ans)