// need #include #include // data structure #include //#include #include #include #include #include #include #include #include //#include //#include #include #include #include //#include #include // stream //#include //#include //#include // etc #include #include #include //#include #include #include #include #define INIT std::ios::sync_with_stdio(false);std::cin.tie(0); #define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__); template void MACRO_VAR_Scan(T& t) { std::cin >> t; } templatevoid MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); } #define VEC_ROW(type, n, ...)std::vector __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int i=0; i void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); } templatevoid MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); } template void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; } templatevoid MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); } #define OUT(d) std::cout< c(n);for(auto& i:c)std::cin>>i; #define MAT(type, c, m, n) std::vector> c(m, std::vector(n));for(auto& r:c)for(auto& i:r)std::cin>>i; #define ALL(a) (a).begin(),(a).end() #define FOR(i, a, b) for(int i=(a);i<(b);++i) #define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i) #define REP(i, n) for(int i=0;i=0;--i) #define FORLL(i, a, b) for(ll i=ll(a);i=ll(a);--i) #define REPLL(i, n) for(ll i=0;i=0;--i) #define PAIR std::pair #define PAIRLL std::pair #define IN(a, x, b) (a<=x && x tmp(a);std::cerr << #a << "\t:";for(int i=0; i(a.size()); ++i){std::cerr << tmp.front() << "\n";tmp.pop();}std::cerr << "\n";} template inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; } template inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; } #define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]" #define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;} void CHECKTIME(std::function f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast((end - start)).count(); std::cerr << "[Time:" << res << "ns (" << res / (1.0e9) << "s)]\n"; } #define int ll using ll = long long; using ull = unsigned long long; constexpr int INFINT = 1 << 30; // 1.07x10^ 9 constexpr int INFINT_LIM = (1LL << 31) - 1; // 2.15x10^ 9 constexpr ll INFLL = 1LL << 60; // 1.15x10^18 constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62); // 9.22x10^18 constexpr double EPS = 1e-7; constexpr int MOD = 1000000007; constexpr double PI = 3.141592653589793238462643383279; bool isPalindromic(const std::string& s) { if (s.size() == 1) return true; size_t sn = s.size(); size_t n = sn / 2; for (size_t i = 0; i < n; ++i) { if (s[i] != s[sn - i - 1]) return false; } return true; } int cnt[11]; signed main() { INIT; FOR(i, 1, 11) { cnt[i] = 9; REP(j, (i - 1) / 2) cnt[i] *= 10; cnt[i] += cnt[i - 1]; } VAR(int, bn); int n = bn; int q = n % 1000000000; n /= 1000000000; std::string s(std::to_string(n)); int res = 0; if (isPalindromic(s)) { if (n <= q) ++res; } n = bn; n /= 1000000000; --n; s = std::to_string(n); int sz = s.size(); auto ss(s); ss.resize((sz + 1) / 2); n = std::stoi(ss); int p = sz / 2; RREP(i, p) { int j = sz - i - 1; if (s[i] == s[j]) continue; if (s[i] > s[j]) --n; break; } res += n; res += cnt[s.size() - 1]; OUT(res)BR; return 0; }