# Example: Calculate NPV
import numpy as np

def calculate_npv(cash_flows, discount_rate):
    return np.npv(discount_rate, cash_flows)

# Example usage
cash_flows = [-1000, 300, 400, 500]
discount_rate = 0.1
npv = calculate_npv(cash_flows, discount_rate)
print(f"NPV: {npv}")