能帮我看看哪里错了吗,老说我运行超时
```c
#include<stdio.h>
int main(){
int n=1;
float i;
float num=1;
float x,sum=0;
scanf("%f",&x);
do{
sum+=num;
num*=n/(2*n+1);
n++;
}while(num>=i);
printf("%.6f",sum*2);
return 0;
}
```