/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static int findKthSmallest (int[] array, int k) {
        if (array == null || array.length == 0 || k <= 0 || k > array.length) {
            throw new IllegalArgumentException("Invalid input");
        }

        return select(array, 0, array.length - 1, k - 1);
    }

    private static int select (int[] array, int start, int end, int k) {
        if (start == end) {
            return array[start];
        }

        int pivotIndex = partition(array, start, end);
        if (k == pivotIndex) {
            return array[k];
        } else if (k < pivotIndex) {
            return select(array, start, pivotIndex - 1, k);
        } else {
            return select(array, pivotIndex + 1, end, k);
        }
    }

    private static int partition (int[] array, int start, int end) {
        int pivot = array[end];
        int i = start - 1;

        for (int j = start; j < end; j++) {
            if (array[j] <= pivot) {
                i++;
                swap(array, i, j);
            }
        }

        swap(array, i + 1, end);
        return i + 1;
    }

    private static void swap (int[] array, int i, int j) {
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }

    public static void main (String[] args) {
        int[] array = { 7, 10, 4, 3, 20, 15 };
        int k = 3;

        int kthSmallest = findKthSmallest(array, k);
        System.out.println("The " + k + "th smallest element is: " + kthSmallest);
    }
}