def collatz (number):
        global st
        st=0
        while number!=1:
            if number%2==0:
                number=number//2
                print(number)
                st=st+1
            elif number%2==1:
                number=3*number+1
                print(number)
                st=st+1
            continue
        print ("Мы получили единичку за", st, "шагов!")

s1 = int(input("Введите целое число: "))
collatz(s1)

def collatz (number):
    global st
    st=0
    while number!=1:
        if number%2==0:
            number=number//2
            print(number)
            st=st+1
        elif number%2==1:
            number=3*number+1
            print(number)
            st=st+1
        continue
    print ("Мы получили единичку за", st, "шагов!")

try:
    s1 = int(input("Введите целое число: "))
except:
    print("Нужно ввести число!")
collatz(s1)

Введите целое число: q
Traceback (most recent call last):
Нужно ввести число!
  File "C:/Users/User/.PyCharmCE2018.1/config/scratches/2.py", line 22, in <module>
    collatz(s1)
NameError: name 's1' is not defined

Process finished with exit code 1