use strict;
use warnings;

my $input = "input.txt";
open my $IN, "<", $input or die "cannot open $input $!";
my $output = "output.txt";
open my $OUT, ">", $output or die "cannot open $output $!";
while (my $line = <$IN>) {
    chomp $line; # remove newline character from end of line
    if ($line =~ /INTERPOLATED HYDROGRAPH AT (\w+)$/){
        print $OUT $1;
        next for 1..5; # skip 5 lines
        my $val2 = (split / /, $line)[1]; get the second column
        print $OUT $val2; # a separator may be needed here
        next; # skip one line
        my $val3 = (split / /, $line)[-1]; # get the last column
        print $OUT "$val3\n"; # a separator may be needed here
    }
}