my %new_pass;
while (<F1>) {
  chomp;
  my @f = split(':', $_);
  $new_pass{$f[0]} = $f[2];
}

##</code><code>##

while (<F2>) {
  chomp;
  my @f = split(':', $_);
  if (exists $new_pass[$f[0]]) {
    $f[1] = $new_pass[$f[0]];
  }
  print F3 join(':', @f), "\n";
}