/*
#include <stdio.h>
int main()
{
double pi = 1.0;
double term = 1.0;
for (int i = 1; term >= 1e-6; i++)
{
term *= i / (2.0 * i + 1);
pi += term;
}
printf("pi的近似值为: %.6lf\n", 2 * pi);
return 0;
}
*/