class Solution {
public:
    int findKthNumber(int m, int n, int k) {
        int lo = 1, hi = m * n;
        while(lo < hi)
        {
            int mid = lo + (hi - lo) / 2;
            int i = count(m, n, mid);
            if(i >= k)
                hi = mid;
            else
                lo = mid + 1;
        }
        return lo;
    }

private:
    int count(int m, int n, int num)
    {
        int i = m, j = 1, res = 0;
        while(j <= n && i > 0)
        {
            while(i * j > num)
                --i;
            res += i;
            ++j;
        }
        return res;
    }
};