CHARACTER(20) S(100)
INTEGER N,M
READ*,N
READ*,S(1)

DO I=2,N
  READ*,S(I)
  M = LEN_TRIM(S(I-1))
  ! LEN_TRIMっていちいち書くの面倒だった
  IF ( S(I-1)(M:M) /= S(I)(1:1) )THEN
    PRINT"(A)","No"
    STOP
  END IF
  
  DO J=1,I-1
    IF ( S(I) == S(J) )THEN
    PRINT"(A)","No"
    STOP 
    ENDIF
  END DO
  
END DO

PRINT"(A)","Yes"

END