sub MI {
    my( $string_es, $string_en, $hash_es, $hash_en ) = @_;

    my $prob_es = ( keys %$hash_es ) / 6939873;
    my $prob_en = ( keys %$hash_en ) / 6939873;

    my $common = 0;
    exists $hash_en->{ $_ } and ++$common for keys %$hash_es;
    
    my $prob_es_en= ( $common ) / 6939873;
    $prob_es_en = ( $prob_es_en + ( $prob_es * $prob_en * 0.1) ) / 1.1;
    
    my $mi = $prob_es_en * log( $prob_es_en / ( $prob_es * $prob_en ) );
    return $mi;
}