According to Wikipedia, Pink Floyd's 5th album was "Atom Heart Mother", released in 1970. The 5 tracks on it are:
"Atom Heart Mother"
"If"
"Summer '68"
"Fat Old Sun"
"Alan's Psychedelic Breakfast"
Pink Floyd's 6th album was
"Meddle", released in 1971 with 6 tracks:
"One of These Days"
"A Pillow of Winds"
"Fearless"
"San Tropez"
"Seamus"
"Echoes"
However, "Meddle" was the 5th studio album.
JimC