// Originally written in 2015

#include<stdio.h>
int main()
{
    int sign=1, n;
    double i, pi=1;
    printf("Enter the value of n: \n");
    scanf("%d", &n);
    for(i=3; i<n; i=i+2)
    {
        sign*=-1;
        pi+=(sign*((double)(1/i)));
        //printf("\n%lf", pi);  // SAME AS pi=pi+( sign* ( (double)(1/i) ) );
    }
    pi*=4;
    printf("The value of pi is: %lf\n", pi);
    return 0;
}

/*
Enter the value of n:
10
The value of pi is: 3.339683

Enter the value of n:
1000
The value of pi is: 3.139593

Enter the value of n:
9999
The value of pi is: 3.141793

Enter the value of n:
99999
The value of pi is: 3.141613

Enter the value of n:
999999
The value of pi is: 3.141595

Enter the value of n:
9999999
The value of pi is: 3.141593

Enter the value of n:
999999999
The value of pi is: 3.141593
 */