#include <algorithm>
#include <cmath>
#include <functional>
#include <iostream>

using namespace std;

int main(int argc, const char* argv[])
{
	uint64_t N;
	cin >> N;
	uint64_t b = (uint64_t)1e9 + 1;
	N /= b;

	//	ある文字列以下の鏡文字
	auto mirror = [](string s) {
		function<uint64_t(string)> f;
		f = [&](string s) {
			if (s.size() == 0) return (uint64_t)0;
			if (s.size() == 1) return (uint64_t)s.front() - '0' + 1;
			uint64_t cnt = 0;
			uint64_t a   = s.front() - '0';
			uint64_t z   = s.back() - '0';
			if (s.size() == 2) return (uint64_t)min(a, z) + 9 + 1;
			s.erase(s.begin());
			s.pop_back();
			uint64_t v = pow(9, max(0, ((int)s.size() - 1) / 2));
			cnt += (uint64_t)min(a, z) * v + f(s);
			return cnt;
		};

		return f(s);
	};

	uint64_t cnt = mirror(to_string(N));
	//	0は倍数の条件は満たすが、1<=???<=Nの条件を満たさない
	cnt -= mirror("0");

	cout << cnt << endl;
	return 0;
}