def calculate_shipping_cost(weight):
    if weight < 1 or weight > 50:
        print("Invalid Input.")
    elif weight <= 5:
        print("100 USD")
    elif weight <= 20:
        print("200 USD")
    else:  weight > 20 and <= 50
        print("300 USD")

# Example usage:
calculate_shipping_cost(3.5)   # Output: 100 USD
calculate_shipping_cost(50.1)  # Output: Invalid Input.