S5= (2058*(1-(1/7)^5)) / (1-1/7)=
(1/7)^5=1/16807
1-(1/7)^5=16806/16807
2058*(1-(1/7)^5)=2058*16806/16807=(делим на 7)=294*16806/2401=4940964/2401
1-1/7=6/7
4940964/2401 / 6/7=4940964/2401 * 7/6= (делим на 6)=823494/2401 *7= (делим на 7)=823494/343=2400 294/343