def calculate_pi(iterations):
    pi_approximation = 0.0
    for i in range(iterations):
        term = 4.0 * (-1) ** i / (2 * i + 1)
        pi_approximation += term
    return pi_approximation

# Number of iterations for approximation
iterations = 1000000
approx_pi = calculate_pi(iterations)
print(f"Approximation of pi after {iterations} iterations: {approx_pi}")