040.cpp

#include <iostream>
using namespace std;

unsigned long pow10(unsigned p)
{
        unsigned long product = 1;
        for (unsigned k=1;k<=p;k++) {
                product*=10;
        }
        return product;
}

long no_of_integers_of_order(unsigned x)
{
        return pow10(x)-pow10(x-1);
}

int d(long k)
{
        int i;
        long last_complete_series=0;
        for (i=1;last_complete_series<k;i++) {
                last_complete_series+=i*no_of_integers_of_order(i);
        }

        i--;
        long incomplete_sequence = k- (last_complete_series-i*no_of_integers_of_order(i));

        long quo = incomplete_sequence / i;
        long ren = incomplete_sequence-quo*i;

        int last_integer = quo+pow10(i-1);
        int position = i-ren;
        
        int digit = (last_integer/pow10(position))%10;
        //cout << last_integer << '\t' << position << endl;
        return digit;


}

int main()
{
        unsigned prod=1;
        for (long i=10;i<=1000000;i*=10)
                prod *= d(i);
        cout << prod << endl;
        return 0;
}