awk to add row # skipping header -

i trying add line number before each row in skipping header using awk. below seems removing header , starting line number @ 2. close? thank :).

input

chr start   end gene chrx 110961329 110961512 alg13 chrx 110987885 110988142 alg13 

awk

awk 'nr>1{print nr, $0}' input 

current output

2 chrx 110961329 110961512 alg13 3 chrx 110987885 110988142 alg13 

desired output

1 chrx 110961329 110961512 alg13 2 chrx 110987885 110988142 alg13 

you should print output when number line 1

$ awk 'nr==1{print $0} nr>1{print nr-1, $0}' input  chr start   end gene 1 chrx 110961329 110961512 alg13 2 chrx 110987885 110988142 alg13