input: Write a python function to create a simple calculator GUI using tkinter, that accepts three inputs and displays their sum.
  assert calculate_sum(1, 2, 3) == 6
  assert calculate_sum(10, 20, 30) == 60
  assert calculate_sum(-1, -2, -3) == -6
output: def create_calculator():
      import tkinter as tk
  
      def calculate_sum():
          num1 = int(entry1.get())
          num2 = int(entry2.get())
          num3 = int(entry3.get())
          result = num1 + num2 + num3
          label_result.config(text="Sum: " + str(result))
  
      root = tk.Tk()
      root.title("Simple Calculator")
  
      label1 = tk.Label(root, text="Number 1:")
      label1.grid(row=0, column=0)
      entry1 = tk.Entry(root)
      entry1.grid(row=0, column=1)
  
      label2 = tk.Label(root, text="Number 2:")
      label2.grid(row=1, column=0)
      entry2 = tk.Entry(root)
      entry2.grid(row=1, column=1)
  
      label3 = tk.Label(root, text="Number 3:")
      label3.grid(row=2, column=0)
      entry3 = tk.Entry(root)
      entry3.grid(row=2, column=1)
  
      button = tk.Button(root, text="Calculate Sum", command=calculate_sum)
      button.grid(row=3, columnspan=2)
  
      label_result = tk.Label(root, text="Sum: ")
      label_result.grid(row=4, columnspan=2)
  
      root.mainloop()
  
  # Example usage:
  create_calculator()