Standards-Based Grading Calculator

grades = [0]
print("Input grades as 2-digit numbers instead of decimals, with the tens place being the ones place and the tenths place being the ones place. When completed, input ;;")
counter_gradenumber = 0
inputgrade = ""
while inputgrade != ";;":
    inputgrade = input("")
    if inputgrade != ";;":
        grades.append(inputgrade)
        counter_gradenumber = counter_gradenumber + 1
if counter_gradenumber <= 1:
  countersave = 1
elif counter_gradenumber > 1:
  countersave = counter_gradenumber + 1
sumgrade = 0
while counter_gradenumber >= 0:
    sumgrade = sumgrade + int(grades[int(counter_gradenumber)])
    counter_gradenumber = counter_gradenumber - 1
actualsumgrade = sumgrade/10
avggrade = actualsumgrade/countersave
finalgrade = (avggrade * 15) + 40
print("Average Standards-Based Grade:")
print(avggrade)
print("Converted to conventional grade:")
print(finalgrade)