#include<iostream> #include<cstdio> #include<cstring> #include <cstdlib> #include <cmath> #include<cctype> #include<string> #include<set> #include<iomanip> #include <map> #include<algorithm> #include <functional> #include<vector> #include<climits> #include<stack> #include<queue> #include <deque> #include <climits> #include <typeinfo> #include <utility> #define all(x) (x).begin(),(x).end() #define rep(i,m,n) for(int i = m;i < n;++i) #define pb push_back #define fore(i,a) for(auto &i:a) #define rrep(i,m,n) for(int i = m;i >= n;--i) #define INF INT_MAX/2 using namespace std; using ll = long long; using R = double; using Data = pair<ll, vector<int>>; const ll MOD = 1e9 + 7; const ll inf = 1LL << 50; struct edge { ll from; ll to; ll cost; }; vector<ll>s; ll conv(string p) { ll ret = 0; reverse(all(p)); ll dgt = 1; fore(x, p) { ret += dgt * (x - '0'); dgt *= 10; } return ret; } ll getdigit(string s) { return s.size(); } int main() { ll n; cin >> n; ll temp = 1e9 + 1; rep(i, 1, 10)s.pb(i); for(ll i = 1; i < 10000; i++) { string s1 = to_string(i); string s2 = s1; reverse(all(s2)); s.pb(conv(s1 + s2)); for (ll j = 0; j <= 9; j++) { s.pb(conv(s1 + to_string(j)+s2)); } } sort(all(s)); ll ans = 0; fore(x,s) { if (x * temp <= n)ans++; } cout << ans << endl; return 0; }