#33 백준 파이썬 [1065] 한 수

#33 백준[1065] 한 수

https://www.acmicpc.net/problem/1065

#Solution

input_num = int(input())
all_numbers = []

for k in range(1, input_num+1):
    if 0 < k < 100:
        all_numbers.append(k)

    elif 100 <= k < 1000:
        number_shape = []
        number_shape = [k // 100, (k // 10) % 10, k % 10]
        if number_shape[0] - number_shape[1] == number_shape[1] - number_shape[2]:
            all_numbers.append(k)

    elif input_num == 1000:
        break

print(len(all_numbers))