652 B | 652 chars
import sys
from math import sqrt, pi, sin, factorial
BLANK = " "
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
n, m = mii()
names = [input() for _ in range(n)]
ans = ""
for i in range(0, m):
d = {}
for name in names:
d[name[i]] = d.get(name[i], 0) + 1
l = sorted(list(d.items()), key = lambda t : (-t[1], t[0]))
ans += l[0][0]
p(ans)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()