n = int(input())

num_count = 0

for i in range(n+1):
    i_str = str(i)
    tar_length = len(i_str)
    i_sqr = i**2
    i_sqr_str = str(i_sqr)
    if i_sqr_str[-tar_length:] == i_str:
        num_count += 1

print(num_count)