668

class Solution {
public:
    int findKthNumber(int m, int n, int k) {
        int rows = m, cols = n, l=1, r = m*n;

        // Binary search on answer space.
        int ans = 0;
        while(l<r){
            int mid = (l+r)/2;
            int count = getCount(mid, rows, cols);
            if(count < k)
                l = mid+1;
            else
                r = mid;
        }
        return l;
    }

    int getCount(int k, int rows, int cols){
        int count = 0, curX = rows-1, curY = 0;
        // Count numbers less-equal k.
        for(int i=1; i<=rows; i++)
            count += min(k/i, cols);
        return count;
    }

};