Name that 30-minute tune...

A program director told me about a call he took from a listener.  The listener asked him, "What was that song you played that goes, 'Da, da, da, dum!  Da, da, da, dum?'"  The program director was amused that the listener referred to such a famous piece as a song but didn't want to burst out laughing; he turned away from the phone to compose himself.  The listener continued singing a substantial portion of the piece's first movement.  When the listener finally paused, the p.d. told him, stifling as much of the chuckle in his voice as he could, that the piece he'd heard was Beethoven's fifth symphony.