백준 1065번: 한수 #Python

N = int(input())

if N < 100:
    print(N)
else:
    count = 99

    for i in range(100, N + 1):
        difference_1 = int(str(i)[0]) - int(str(i)[1])
        difference_2 = int(str(i)[1]) - int(str(i)[2])

        if difference_1 == difference_2:
            count += 1

    print(count)