n = int(input())

def func(i):
    stri = str(i**2)
    if stri.endswith(str(i)):  # 是否以某个字符串结尾，参数需要是字符串
        return True
    else:
        return False

counter = 0
for i in range(n+1):
    if func(i):
        counter += 1
print(counter)