sub existElement {
    my $element = shift;
    my $arr = shift;
    for (my $i = 0; $i <= scalar(@$arr) - 1; $i++){
        if ($arr->[$i] eq $element) {
            return ($arr->[$i] eq $element) ? 1 : 0;
            last;
        }        
    }
}

sub stringConstruction {
    my @s = split("", shift);
    my $res = [0];
    my $cnt = 0;
    foreach my $el (@s) {
        if (!existElement($el, $res)) {
            push(@$res, $el);
            $cnt++;
        }        
    }
    return $cnt;
}