func_code_string: #include <bits/stdc++.h>   using namespace std;   string int_to_string(int a) {     stringstream ss;     ss << a;     return ss.str();   }   string double_to_string(double a) {     stringstream ss;     ss << a;     return ss.str();   }   string float_to_string(float a) {     stringstream ss;     ss << a;     return ss.str();   }   string long_to_string(long a) {     stringstream ss;     ss << a;     return ss.str();   }   string long_long_to_string(long long a) {     stringstream ss;     ss << a;     return ss.str();   }   int string_to_int(string s) { return atoi(s.c_str()); }   float string_to_float(string s) { return atof(s.c_str()); }   long string_to_long(string s) { return atol(s.c_str()); }   long long string_to_long_long(string s) { return atoll(s.c_str()); }   int main() {     long long n, c = 0;     cin >> n;     for (long long i = 1; i <= n; i *= 10) c += (n - (i - 1));     cout << c;     return 0;   }   