Why is my recursive function so slow in R?

The following takes about 30 seconds to run whereas I would expect it to be nearly instant. Is there a problem with my code?

x <- fibonacci(35);

fibonacci <- function(seq) {
    if (seq == 1) return(1);
    if (seq == 2) return(2);
    return (fibonacci(seq - 1) + fibonacci(seq - 2));
}