Add number of days to date based on a condition

Are you able to help, I have a starting date of 07/06/2017 in cell H4, I then want to add the number of days which is in columns C but only if there is a Yes in column D, this works but not if there is a NO. If there is a No, I want it to look at the last date that was calculated e.g. 14/06/2017 and then carry on. I have attached the file.