#!python3
import sys
n, m = [int(v) for v in input().split(' ')]
dat = [0 for _ in range(m)]
st = [0 for _ in range(m+1)]
for i in range(n):
   s = input()
   for j in range(len(s)):
      if s[j] == '1':
         dat[j] |= 1<<i
r = m
def recur(at, bc, t):
   global r
   if t < bc:
      r = min(t, r)
   while t < r and at < m:
      st[bc+1] = st[bc] | dat[at]
      recur(at+1, bc+1, int.bit_count(st[bc+1]))
      at += 1
recur(0, 0, 0)
print(r)