How to remove duplicated columns with the same value regardless of the column names in R?

Question

Input:

a<- c(1,2,2)
b<- c(1,2,2)
c<- c(1,2,3)
d<- c(0,0,0)
e<- c(0,0,0)

f<- cbind(a,b,c,d,e)

What I want (look at the outc