import java.io.BufferedInputStream; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.*; public class _491 { public static void main(String[] args) throws IOException { new _491().solve(); } void solve() throws IOException { try (final Scanner in = new Scanner(System.in)) { n = in.nextLong(); long ans = 0; for (int i = 1; i <= 9; i++) { ans += rec(i, 0, 0); } System.out.println(ans); } } long n; char[] cs; long x = 1000000000+1; long rec(int len, int idx, long cur) { if (len % 2 == 0) { if (2*idx == len) { long c = cur; for (int i = 0; i < len / 2; i++) { cur = cur * 10 + c % 10; c /= 10; } // if (cur * x <= n) dump(cur); return cur * x <= n ? 1 : 0; } } else { if (2*idx-1 == len) { long c = cur; for (int i = 0; i < len / 2; i++) { cur = cur * 10 + c % 10; c /= 10; } // if (cur * x <= n) dump(cur); return cur * x <= n ? 1 : 0; } } long ans = 0; for (int i = 0; i < 10; i++) { if (cur == 0 && i == 0) continue; ans += rec(len, idx + 1, cur * 10 + i); } return ans; } // for debug static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); } }