def replace():
    global sentence
    while sentence.count("a")>0:
        sentence = sentence[0:sentence.index("a")] + "@" + sentence[sentence.index("a")+1: len(sentence)]
        replace()
        
sentence = input("Write a sentence containing an a: ")
replace()
print(sentence)

80ed3628659d011e81b3d32e51ad5c53c25722bb
<mask token>

def replace():
    global sentence
    while sentence.count('a') > 0:
        sentence = sentence[0:sentence.index('a')] + '@' + sentence[
            sentence.index('a') + 1:len(sentence)]
        replace()


<mask token>

def replace():
    global sentence
    while sentence.count('a') > 0:
        sentence = sentence[0:sentence.index('a')] + '@' + sentence[
            sentence.index('a') + 1:len(sentence)]
        replace()


<mask token>
replace()
print(sentence)

def replace():
    global sentence
    while sentence.count('a') > 0:
        sentence = sentence[0:sentence.index('a')] + '@' + sentence[
            sentence.index('a') + 1:len(sentence)]
        replace()


sentence = input('Write a sentence containing an a: ')
replace()
print(sentence)

def replace():
    global sentence
    while sentence.count("a")>0:
        sentence = sentence[0:sentence.index("a")] + "@" + sentence[sentence.index("a")+1: len(sentence)]
        replace()
        
sentence = input("Write a sentence containing an a: ")
replace()
print(sentence)
