`F = 1/2 + 1/14 + 1/35 + 1/64 + 1/104 + 1/152`
`F = 2/4 + 2/28 + 2/70 + 2/130 + 2/208 + 2/304`
`F = 2/(1 . 4) + 2/(4 . 7) + 2/(7 . 10) + 2/(10 . 13) + 2/(13 . 16) + 2/(16 . 19)`
`F = (3/(1 . 4) + 3/(4 . 7) + 3/(7 . 10) + 3/(10 . 13) + 3/(13 . 16) + 3/(16 . 19)) : 3/2`
`F = (1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + 1/13 - 1/16 + 1/16 - 1/19) : 3/2`
`F = (1 - 1/19) : 3/2`
`F = 18/19 : 3/2`
`F = 12/19`