bash - Print result to every second line of output file in awk -

seems no 1 yet stumbled upon problem,so here goes.
sets say,i want take third column $3 of every other line 2nd,4th,6th etc of input file(i know how that) , print result @ same position in output file.
mean,$3 of 2nd line of input,to $3 of 2nd line of output , goes on.

i want this,using awk bash.

here how awk

awk 'fnr==nr {a[nr]=$3;next} fnr%2==0 {$3=a[fnr]}1' firstfile secondfile 

this take data firstfile , update secondfile using column $3 , every second line.
data replaced in same position.

cat firstfile 1 one green 2 two red 3 three blue 4 four orange 5 five yellow 6 six brown 

cat secondfile 1 one jan 2 two feb 3 three mars 4 four april 5 five jun 6 six juli 

running awk command:

1 1 jan 2 two red 3 three mars 4 four orange 5 five jun 6 six brown 

too store data secondfile

awk 'fnr==nr {a[nr]=$3;next} fnr%2==0 {$3=a[fnr]}1' firstfile secondfile > tmp && mv tmp secondfile