35cm!
4 + 4 = 8
7 + 7 = 14
13 + 8 = 21 (13 + (8 - 1 ) = 20 + 1 = 21)
21 + 14 = 35 (4 + 1 = 5, 20 + 10 = 30, 30 + 5 = 35)
