[R] Conditions

[Val]

HI All, I am having a little issue in my ifelse statement,
The data frame looks like as follow.

dat2 <-read.table(text="ID  d1 d2 d3
A 0 25 35
B 12 22  0
C 0  0  31
E 10 20 30
F 0  0   0",header=TRUE,stringsAsFactors=F)
I want to create d4 and set the value based on the following conditions.
If d1  !=0  then d4=d1
if d1 = 0  and d2 !=0  then d4=d2
if (d1  and d2 = 0) and d3  !=0 then d4=d3
if all d1, d2 and d3 =0 then d4=0

Here is the desired output and my attempt
 ID d1 d2 d3 d4
  A  0 25 35  25
  B 12 22  0  12
  C  0  0 31   31
  E 10 20 30  10
  F  0  0  0  0  0

My attempt
dat2$d4 <-  0
dat2$d4  <- ifelse((dat2$d1 =="0"), dat2$d2, ifelse(dat2$d2 == "0"), dat2$d3, 0)
but not working.

Thank you.