How to fix the overlap problem of coordinate x axis

[DDyao]

library(ggplot2) Date <- c('30-05-2015','30-06-2015','4-10-2015','5-1-2015','5-3-2015','17-4-2015','17-05-2015','19-04-2015','19-05-2015','6-9-2015') freq <- c(9,63,21,12,5,21,7,9,12,23)

count_date <- data.frame(Date,freq)

ggplot(count_date, aes(Date,freq)) + geom_point() + geom_line(aes(group=Date)) + xlab("Date") + ylab("No. of Complaints")