func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     std::ios_base::sync_with_stdio(false);     long long n;     cin >> n;     long long nmax = 9999999999;     while ((nmax / 2) >= n) nmax /= 10;     int inc = nmax + 1;     long long ans = 0;     if (nmax == 0) {       ans = (n * (n - 1)) / 2;       cout << ans << endl;       return 0;     }     while (n >= (nmax / 2)) {       cerr <<  ans             <<   is   << ans << endl;       ;       if (n >= nmax)         ans += (nmax / 2);       else         ans += n - (nmax / 2);       nmax += inc;     }     cout << ans << endl;     return 0;   }   