Brush questions - Luogu -p1035 series summation

P1035 Sum of series -C Language

1、 subject

2、 The problem solving process

(1) for the first time sacnf_s Because of the use of vs2019 The compiler of runs
result ：Unaccepted
reason ： It should be used in Luogu int main() +return 0

（2） The second time
result ：60 branch
reason ： Accuracy should be considered

(3) third time
result ：Accepted