不会运行了。！？，…

#include <stdio.h>
int main(){
  int n;
  double sum=0;
  scanf("%d",&n);
for(int i=0;i<n;++i){
    sum+=1.0/(3*(i+1)-2);
}
  printf("%.5f",sum);
}

#include <stdio.h>
#include<iostream>
int main()
{
    int n;
    double sum=0;
    scanf("%d",&n);
    for (int i = 1; i <=(3*n-2) ; i+=3)
    {
       sum+=1.0/i;
    }
    printf("%.5f",sum);
    system("pause");
    return 0;
}