def func(x):
    a = str(x * x) 
    b = len(str(x))
    if x == int(a[-b:]):
        return True
    else:
        return False 



while True: 
    try:
        n = int(input())
        num = 0
        for x in range(n+1):
            if func(x):
                num += 1
            else:
                continue
        print(num)
    except:
        break