Which opera  Pelléas et Mélisande and Die schweigsame Frau has fewer acts ?
Pelléas et Mélisande (opera) Pelléas et Mélisande ("Pelléas and Mélisande") is an opera in five acts with music by Claude Debussy. The French libretto was adapted from Maurice Maeterlinck's Symbolist play "Pelléas et Mélisande". It premiered at the Opéra-Comique in Paris on 30 April 1902 with Jean Périer as Pelléas and Mary Garden as Mélisande in a performance conducted by André Messager, who was instrumental in getting the Opéra-Comique to stage the work. The only opera Debussy ever completed, it is considered a landmark in 20th-century music.
L'Olimpiade (Pergolesi) L'Olimpiade is an opera in the form of a dramma per musica in three acts by the Italian composer Giovanni Battista Pergolesi. Pergolesi took the text, with a few modifications, from the libretto of the same name by Pietro Metastasio. The opera first appeared during the Carnival season of 1735 at the in Rome and "came to be probably the most admired" of the more than 50 musical settings of Metastasio’s drama.