#include <stdio.h>

main()
{
	double pi;
	int K;
	int k;

	printf("Enter the degree of approximation: ");
	scanf("%d", &K);

	for (k = 0, pi = 0.0; k <= K; k++) {

		if (k % 2 == 0) /* k is even */
			pi = pi + 4 / (2 * k + 1);
		else /* k is odd */
			pi = pi - 4 / (2 * k + 1);
	}

	printf("The value of pi is: %11.9f\n", pi);
}