#include<algorithm> #include<iostream> #include<cmath> using namespace std; long long f(int k) { if (k < 10) return k; if (k % 10 == 0) return f(k - 1) + log10(k) + 1; int cnt = 1; while (k > static_cast<int>(pow(10, cnt))) ++cnt; --cnt; return f(pow(10, cnt)) + (cnt + ...