#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define FOR(i,a,b) for(int i=(a);i<(b);i++) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() template inline bool chmax(A &a, B b) { if (a inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; } typedef long long ll; typedef pair pii; typedef pair pll; typedef pair P; typedef vector vl; typedef vector vvl; #define INF (1<<29) #define INFL (1ll<<60) #define EPS (1e-8) #define PI (acos(-1)) const ll MOD = 1000000007ll; string to_str(ll x) { stringstream ss; ss << x; return ss.str(); } ll to_ll(string str) { stringstream ss(str); ll res; ss >> res; return res; } bool ispd(string str) { REP(i, str.size() / 2) if (str[i] != str[str.size() - 1 - i]) return false; return true; } int main() { ll N; cin >> N; ll n = N / 1000000001; vector v; for (ll i = 1; i <= 100000; i++) { string now = to_str(i); string rev = now; reverse(ALL(rev)); string tmp = now.substr(0, now.size() - 1) + rev; if (ispd(tmp) && tmp.size() < 10) v.push_back(to_ll(tmp)); if (!ispd(now)) continue; tmp = now + rev; if (tmp.size() < 10) v.push_back(to_ll(tmp)); } //cout <<"before:" << v.size() << endl; sort(ALL(v)); v.erase(unique(ALL(v)), v.end()); //cout <<"after: " << v.size() << endl; int ans = 0; REP(i, v.size()) { if (v[i] <= n) ans++; } cout << ans << endl; return 0; }