use strict;
use warnings;

my $firsttime = 1;

my $line1 = <DATA>;
print neverflop();
$firsttime = 0;

my $line2 = <DATA>;
print neverflop();

scalar tell(STDIN);
print neverflop();
print neverflop();

sub neverflop {
   ($firsttime .. 0) ? "flip" : "flop";
}
__DATA__
line1
line2
line3
__END__
Output:
flipflipflipflop