Error longer object length is not a multiple of shorter object length

I have data frames 1&2

df1                               df2
Name    value     age              Name     value1
A        NA        24              A           22
A        34        35              B           39
B        NA        27
C        36        23

Now I want replace NA from df2 in df1.

I tried to replace with below

df1$value = ifelse(is.na(df1$value) & which(df1$Name %in% df2$Name),df2$value1 , df1$value)

Please suggest any modifications.

o/p
df1
Name    value     age
A        22        24
A        34        35
B        39        27
C        36        23