How to create a variable based on another using if statement in R

I need in 2nd column a count of how many times observation is in 1st column. Here, 2nd column should have values 1,2,3,1,2,1,2. This code doesn't work.

x <- c(11,11,11,22,22,33,33) y <- c(1,1,1,1,1,1,1) df <- data.frame(x,y)

i <- 1    for (i in 1:(nrow(df)-1)){
if(df[i+1,1] == df[i,1]){df[i+1,2] <- 2}
 if(df[i+2,1] == df[i,1]){df[i+2,2 <- 3}
  else df[i+2,2] <- 1}