Fibonacciho_posloupnost <- function(n) {
    if(n < 0 | round(n) - n != 0) return(paste("chybne cislo"))
    if (n == 0) {return(0)}
    if (n == 1) {return(1)}
    a <- 0
    b <- 1
    for (i in seq(2, n, by = 1)) {
        c <- a + b
        a <- b
        b <- c
    }
    return(b)
}