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.
Der Ring des Nibelungen Der Ring des Nibelungen (The Ring of the Nibelung), WWV 86, is a cycle of four German-language epic music dramas composed by Richard Wagner. The works are based loosely on characters from the Norse sagas and the "Nibelungenlied". The composer termed the cycle a "Bühnenfestspiel" (stage festival play), structured in three days preceded by a " " ("preliminary evening"). It is often referred to as the Ring Cycle, "Wagner's Ring", or simply "The Ring".