R: Get dataframe of index values that are outliers

Question

I have a dataset with 170 variables and the first one is Customer ID which I converted as index of the data frame:

input2 <- data.frame(input2[,-1], row.names = input2[,1])

I already found the outliers:

   outliers <- boxplot(input2)$out

but now I want to create a data frame where I have the Customer ID that are considered outliers. How can I get this since the output of "outliers" is a list?

Edit: I tried

which(input2 %in% outliers)

but it gives "integer(0)" as output

Thanks