Ifelse statement in R with multiple conditions

With the following sample data I'm trying to create a new variable "Den" (value "0" or "1") based on the values of three conditional variables (Denial1, Denial2, and Denial3).

I want a "0" if ANY of the three conditional variables has a "0" and a "1" only if EACH conditional variable that has a value in it has a value of "1" (e.g., isn't NA).

structure(list(Denial1 = NA_real_, Denial2 = 1, Denial3 = NA_real_, 
Den = NA), .Names = c("Denial1", "Denial2", "Denial3", "Den"
), row.names = 1L, class = "data.frame")

I've tried both of the following commands that result in a missing value NA for "Den":

DF$Den<-ifelse (DF$Denial1 < 1 | DF$Denial2 < 1 | DF$Denial3 < 1, "0", "1")

DF$Den<-ifelse(DF$Denial1 < 1,"0", ifelse (DF$Denial2 < 1,"0", ifelse(DF$Denial3 < 1,"0", "1")))

Could someone demonstrate how to do this?