def collect_grades():
    grades = []
    print('Enter a score on an exam. If the weight is different than x/100 specify using (grade)/(weight).')
    while True:
        _input = input('''Enter a score on an exam. ( 93 OR 93/100)\n(Press enter to stop):\n''')
        if len(_input) == 0:
            break
        grades.append(_input)
    return grades

if __name__ == '__main__':
    print(collect_grades())

exam1_grade = float(input('Enter score on Exam 1 (out of 100):\n'))
exam2_grade = float(input('Enter score on Exam 2 (out of 100):\n'))
exam3_grade = float(input('Enter score on Exam 3 (out of 100):\n'))

overall_grade = (exam1_grade + exam2_grade + exam3_grade) / 3

print('Your overall grade is:', overall_grade)