백준 2960 에라토스네스의 체

B_2960.java

import java.util.Scanner;

public class Main {	
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
    	
        boolean[] isPrime = new boolean[n+1];
        for(int i = 2; i <= n; i++) {
            isPrime[i] = true;
        }
    	
        int cnt = 0;
    	
        for(int i = 2; i <= n; i++) {
            for(int j = i; j <= n; j += i) {
                if(!isPrime[j]) continue;
                isPrime[j] = false;
                ++cnt;
                if(cnt == k) {
                    System.out.println(j);
                    System.exit(0);
                }
            }
        }
    }
}