(define N (read))
(define M (read))
(define v (make-vector M 0))
(dotimes [i N]
         (read-line)
         (dotimes [j M]
                  (when (char=? (read-char) #\x)
                        (inc! (vector-ref v j)))))
(print (+ 1 (fold max 0 (vector->list v))))