from __future__ import print_function
import sys

m, s    = map(int, sys.stdin.readline().split())
prefs   = [ map(int, line.split()) for line in sys.stdin ]
inits   = [ set() for x in xrange(m) ]
answer  = set()

for j in xrange(s):
  for i in xrange(m): answer.add(prefs[i][j])
  all_ok = True
  for i in xrange(m):
    inits[i].add(prefs[i][j])
    if len(inits[i]) != len(answer): all_ok = False
  if all_ok: break
  
print(len(answer)); print(" ".join(map(str, sorted(answer))))