import sys

for line in sys.stdin:
    a = int(line.rstrip())
    list1 = []
    n=0
    for i in range(a+1):
        #if str(i) == str(i*i):
        if str(i*i)[-len(str(i)):] == str(i):
            n+=1
    print(n)

str(i*i)[-len(str(i)):] == str(i) 一个数是否等于另一个数的末尾