import math

def calculate_area(shape):
    if shape == "circle":
        radius = float(input("Enter the radius of the circle: "))
        area = math.pi * radius ** 2
        print("The area of the circle is:", area)
    elif shape == "rectangle":
        length = float(input("Enter the length of the rectangle: "))
        width = float(input("Enter the width of the rectangle: "))
        area = length * width
        print("The area of the rectangle is:", area)
    elif shape == "triangle":
        base = float(input("Enter the base of the triangle: "))
        height = float(input("Enter the height of the triangle: "))
        area = 0.5 * base * height
        print("The area of the triangle is:", area)
    else:
        print("Invalid shape! Please try again.")

shape = input("Enter the shape (circle, rectangle, or triangle): ")
calculate_area(shape)