Using n() at the same time as calculating other summary statistics

I am having trouble to prepare a summary table using dplyr based on the data set below:

set.seed(1)
df <- data.frame(rep(sample(c(2012,2016),10, replace = T)),
                 sample(c('Treat','Control'),10,replace = T),
                 runif(10,0,1),
                 runif(10,0,1),
                 runif(10,0,1))

 colnames(df) <- c('Year','Group','V1','V2','V3')

I want to calculate the mean, median, standard deviation and count the number of observations by each combination of Year and Group.

I have successfully used this code to get mean, median and sd:

summary.table = df %>% 
    group_by(Year, Group) %>%
    summarise_all(funs(n(), sd, median, mean))

However, I do not know how to introduce the n() function inside the funs() command. It gave me the counting for V1, V2 and V3. This is quite redundant, since I only want the size of the sample. I have tried introducing

    mutate(N = n()) %>%

before and after the group_by() line, but it did not give me what I wanted.

Any help?

EDIT: I had not made my doubt clear enough. The problem is that the code gives me columns that I do not need, since the number of observations for V1 is sufficient for me.