#include<stdio.h>

void fun(float t)
{
double sum = 1.0;
double q = 1.0;
double x;
int n = 1;
while (q>=t)
{
 q=q*(n/(2*n + 1));
 sum += q;
 n++;
}

 x= sum/2;
printf("x = %f\n",x);
}

void main(void)
{
float t;

printf("输入精度\n");
scanf("%d",&t);
fun(t);
}