#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int,int> pint;
typedef vector<pint> vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define all(v) (v).begin(),(v).end()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
const int MOD = 1e9 + 7;
const int INF = 1e9;
const ll INFF = 1e18;

vector<string> tmp;
void dfs(string s, int cnt, int size){
	// cout << s << endl;
	if(cnt == size){
		tmp.pb(s);
		return;
	}
	if(size % 2 == 1 && cnt == size / 2){
		if(size >= 2){
			rep(i, 10){
				string d = to_string(i);
				dfs(s + d, cnt + 1, size);
			}
		}else{
			reps(i, 1, 10){
				string d = to_string(i);
				dfs(s + d, cnt + 1, size);
			}
		}
	}

	if(cnt < size / 2){
		if(cnt != 0){
			rep(i, 10){
				string d = to_string(i);
				dfs(s + d, cnt + 1, size);
			}
		}else{
			reps(i, 1, 10){
				string d = to_string(i);
				dfs(s + d, cnt + 1, size);
			}
		}
	}

	if(cnt >= size / 2){
		auto d = s[size - cnt - 1];
		// cout << "last " << s + d << endl;
		dfs(s + d, cnt + 1, size);
	}
	return;
}

ll solve(ll n){
	ll ret = 0;
	string s = to_string(n);
	reps(i, 1, s.size()){
		if(i % 2 == 0) ret += pow(9, i / 2);
		else ret += pow(9, i);
	}
	// printf("tret %lld\n", ret);
	/*
	ll tmp = 1;
	bool flag = false;
	rep(i, s.size() / 2 + 1){
		ll d = min(s[i] - '0', s[s.size() - i - 1] - '0');
		printf("i %d d %lld\n", i, d);
		if(d != 0) flag = true;
		tmp *= d;
		if(s.size() % 2 == 0 && i == s.size() / 2 - 1) break;
	}
	if(flag) ret += tmp;
	return ret;
	*/
	// dfs("", 0, s.size());
	reps(i, 1, 10){
		auto d = to_string(i);
		dfs(d, 1, s.size());
	}

	for(string u : tmp){
		// cout << "u " << u << endl;
		if(stoll(u) <= n) ret++;
	}
	return ret;
}

int main(void){
	ll n; cin >> n;
	n /= (INF + 1);
	// printf("%lld\n", n);
	printf("%lld\n", solve(n));
	return 0;
}
/*
1000000001
9000000009
11000000011
*/