5  From Levitin's example
a
b
c
d
e

"a" "b" 3
"a" "c" 1
"a" "d" 5
"a" "e" 8
"b" "c" 6
"b" "d" 7
"b" "e" 9
"c" "d" 4
"c" "e" 2
"d" "e" 3