class Solution {
    public int findKthNumber(int m, int n, int k) {
        int lo = 1;
        int hi = m * n;

        while (lo < hi - 1) {
            int mid = lo + (hi - lo) / 2;
            if (d(mid) < k) lo = mid;
            else hi = mid;
        }

        System.out.println(lo);

        int s = d(lo);
        int x = lo + 1;
        while (s < k) s += theta(x++);

        return x -1;
    }

    private int d(int x) {
        int u = 1;
        while (u*u <= x) u++;
        u--;

        int s = 0;
        for (int k = 1; k <= u; k++) s += 2 * (x / k);
        s -= u*u;

        return s;
    }

    private int theta(int x) {
        if (x == 1) return 1;

        int u = 1;
        while (u*u <= x) u++;
        u--;

        int num = 0;
        for (int k = 1; k <= u; k++)
            if (x % k == 0) num += 2;

        if (x == u*u) num--;

        return num;
    }
}