#include <bits/stdc++.h>
using namespace std;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

int main() {
    constexpr int64_t base = 1000000001;

    int64_t n; cin >> n;

    int ans = 0;
    for (int i = 1; i < 100000; ++i) {
        auto s1 = to_string(i);
        auto s2 = s1;
        auto s3 = s1.substr(0, s1.size() - 1);
        reverse(begin(s2), end(s2));
        reverse(begin(s3), end(s3));

        auto n1 = s1 + s2;
        auto n2 = s1 + s3;

        if (n1.size() <= 9) {
            ans += base * stol(n1) <= n;
        }
        if (n2.size() <= 9) {
            ans += base * stol(n2) <= n;
        }
    }

    cout << ans << endl;
}