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(m, n) = map(int, raw_input().split())
res = []
for i in range(n):
    ins = map(int, raw_input().split())
    res = res + [(val, i) for val in ins]
# print(res)
res = sorted(res)
help = [[] for i in range(n)]
for idx, (val, i) in enumerate(res):
    help[i].append(idx)
present = [0] * n 
small = float('inf')
# end = [m - 1] * n
# print(res)
while True:
    index_list = [help[idx][idy] for idx, idy in enumerate(present)]
#    print(present)
    max_, min_ = max(index_list), min(index_list)
    small = min(small, res[max_][0] - res[min_][0])
    present[index_list.index(min_)] += 1
#    print(present)
#    print('---')                                                                                                                                                                                                  
    if present[index_list.index(min_)] == m:
        break
print(small)
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