10427.cpp

#include <bits/stdc++.h>

using namespace std;

int get_digit(int n, int d)
{
	int digits[9];
	for (int i = int(log10(n)); i >= 0; i--)
	{
		digits[i] = n % 10;
		n /= 10;
	}
	return digits[d];
}

int main()
{
	int n, i;
	int sum, tmp, num;
	int count[9] = {0, 9, 90, 900, 9000, 90000, 900000, 9000000, 90000000};
	while (cin >> n)
	{
		sum = 0;
		if (n < 10)
		{
			cout << n << endl;
			continue;
		}
		for (i = 1; i <= 8; i++)
		{
			sum += i * count[i];
			if (sum >= n)
			{
				break;
			}
		}
		for (int j = 0; j < i; j++)
		{
			n -= j * count[j];
		}
		tmp = (n % i == 0 ? n / i - 1 : n / i);
		num = (i == 1 ? 0 : int(pow(10, i - 1))) + tmp;
		tmp = (n % i == 0 ? i - 1 : n % i - 1);
		cout << (i == 1 ? num : get_digit(num, tmp)) << endl;
	}
	return 0;
}