use warnings;
use strict;

my $protein;

while (<DATA>) {
    if (/^>/) {
        next;
    }
    else {
        $protein = join '', split;
    }
}

my $number_of_F = grep { /F/ } split //, $protein;

print "The aminoacid sequence: ", $protein, " contains ", $number_of_F,
  " Phenylalanine aminoacids", $/;

__DATA__
>gi|403369491|gb|EJY84591.1| Transcriptional regulator, Sir2 family protein Oxytricha trifallax

MMKQLIKHNKNTPLFNFLRVKFSSTAATIQTQQTVNKPIESKFKEEKLDNYHDIYEKSKRLAEQISQSKS FICFTGAGLSTSTGIPDYRSTSNTLAQTGAGAYELEISEEDKKSKTRQIRSQVQRAKPSISHMALHALME NGYLKHLISQNTDGLHLKSGIPYQNLTELHGNTTVEYCKSCSKIYFRDFRCRSSEDPYHHLTGRQCEDLK CGGELADEIVHFGESIPKDKLVEALTAASQSDLCLTMGTSLRVKPANQIPIQTIKNKGQLAIVNLQYTPF DEIAQIRMHSFTDQVLEIVCQELNIKIPEYQMKRRIHIIRNAETNEIVVYGSYGNHKNIKLSFMQRMEYI DNKNHVYLALDKEPFHIIPDYFNFQNINTDQEEVEFRIHFYGHNSEPYFQLTLPRQSILELQAGEHLICD ITFDYDKLEWK