한수

#include <iostream>
using namespace std;

int main()
{
	int num, count;
	int a, b, c;

	cin >> num;

	if (num < 100)
		cout << num << '\n';
	else
	{
		count = 0;
		for (int i = 100; i <= num; i++)
		{
			a = i / 100;
			b = (i % 100) / 10;
			c = i % 10;

			if ((a - b) == (b - c))
				count++;
		}
		cout << count + 99 << '\n';
	}
	return 0;
}