value = int(eval(input()))

count = 0

while value > 0:

    if len(str(value)) % 2 != 0:

        count += 1

    value -= 1

print(count)
def main():

    value = int(eval(input()))

    count = 0

    while value > 0:

        if len(str(value)) % 2 != 0:

            count += 1

        value -= 1

    print(count)

if __name__ == "__main__":

    main()
value = int(eval(input()))
count = 0
while value > 0:
    if len(str(value)) % 2 != 0:
        count += 1
    value -= 1
print(count)

def main():
    value = int(eval(input()))
    count = 0
    while value > 0:
        if len(str(value)) % 2 != 0:
            count += 1
        value -= 1
    print(count)


if __name__ == "__main__":
    main()

-value = int(eval(input())) -count = 0 -while value > 0: -    if len(str(value)) % 2 != 0: -        count += 1 -    value -= 1 -print(count) +def main(): +    value = int(eval(input())) +    count = 0 +    while value > 0: +        if len(str(value)) % 2 != 0: +            count += 1 +        value -= 1 +    print(count) + + +if __name__ == "__main__": +    main()