#include<stdio.h>
#include<conio.h>
#include<math.h>
main()
{
float pi, e;
int i;
do
{ printf("\n Nhap epsilon e= "); scan("%f",&e);
}while(1<e||0>e);
pi=1;
i=1;
while((1.0/(2*i+1)<e)
{pi=4*(pi+pow(-1,i)*(2*i+1));
i++;}
printf(" so pi la : %f",pi);
getch();
}