12번

#include<iostream>
using namespace std;

int main()
{
	int c = 1, d = 9, res = 0,sum=0;
	int N;
	cin >> N;
	while (sum + d < N)
	{
		sum = c * d;
		res = res + sum;
		c++;
		d = d * 10;
	}
	cout << res + (N - res)*c;
	
}