// thread.cpp

#include <math.h>

#include <iostream>
#include <thread>

#define nMaxDefault 100000000  // default
//#define nMax 85765682        // for T(s) = 200
//#define nMax 1640000000      // for T(s) = 400

unsigned nMax = nMaxDefault;
unsigned nMaxSqrt;
unsigned short* v;

static void odd()
{
    for (int i = 7; i < nMaxSqrt; i += 2)
    {
        int k2 = i + 3;
        int k3 = i + i - 4;
        while ((k2 <= k3) && ((i * k2) < nMax))
        {
            int k4 = (nMax - 1) / i;
            if (k3 < k4)
                k4 = k3;
            for (int j = k2; j <= k4; j += 2)
                ++v[(i * j) / 2];
            k2 += i + 1;
            k3 += i - 1;
        }
    }
}

static void even()
{
    for (int i = 8; i < nMaxSqrt; i += 2)
    {
        int k2 = i + 3;
        int k3 = i + i - 4;
        while ((k2 <= k3) && ((i * k2) < nMax))
        {
            int k4 = (nMax - 1) / i;
            if (k3 < k4)
                k4 = k3;
            for (int j = k2; j <= k4; ++j)
                ++v[(i * j) / 2];
            k2 += i + 1;
            k3 += i - 1;
        }
    }
}

int Tatami(int s)
{
    v = new unsigned short[nMax / 2];
    for (unsigned i; i < (nMax / 2); i++)
        v[i] = 0;
    nMaxSqrt = sqrt(nMax);

    std::thread evenThread(even);
    std::thread oddThread(odd);
    evenThread.join();
    oddThread.join();

    for (int i = 0; i < nMax / 2; ++i)
        if (v[i] == s)
            return i + i;
    return 0; // shouldn't happen
}

int main(int ac, char* av[])
{
    int s = atoi(av[1]);
    if (ac > 2)
        nMax = strtoul(av[2], NULL, 10);
    std::cout << "T(" << Tatami(s) << ") = " << s << std::endl;
}