myfun <- function (x) {
UseMethod("myfun")
}

myfun.numeric <- function(x) {
  a<-x+5
  b<-a^2
  c<-b+4
  d<-c-3
  d
}

myfun.character <- function(x) {
  a<-as.numeric(x)+9
  b<-a^2
  c<-b+4
  d<-c-3
  d
}

myfun("3")
myfun(3)