n = int(input())

left = 1
right = 10**5 + 10

def check(mid):
    if (10**(mid - 1))**2 <= n:
        return True
    else:
        return False

while right - left > 1:
    mid = (right + left) // 2
    if check(mid):
        left = mid
    else:
        right = mid

print(left)