Create an app on android studio to calculate the factorial of a number

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. For example,

5! = 5 * 4 * 3 * 2 *1 = 120

The app should allow user to enter a number and click on Submit button to see the answer; if the user input is less than 1, display a toast message Enter a number greater than 0