Write a python function to find the first digit of a given number.
def first_Digit(n) :  
    while n >= 10:  
        n = n / 10; 
    return int(n) 
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a python function to find the first digit of a given number.
def first_Digit(n) :  
    while n >= 10:  
        n = n / 10; 
    return int(n) [/INST]assert first_Digit(123) == 1
assert first_Digit(456) == 4
assert first_Digit(12) == 1</s>