[BOJ] 백준 3343 장미

범위 주의 !

 

 

[문제]

https://www.acmicpc.net/problem/4948

 

 

[소스 코드]

import java.io.*;
import java.util.*;
public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		while(true) {
			int n = Integer.parseInt(br.readLine());
			if(n==0) break;
			if(n==1) {
				System.out.println(1);
				continue;
			}
			int result = 0;
			boolean[] prime = new boolean[2*n+1];
			Arrays.fill(prime,true);
			for(int i=2;i*i<=2*n;i++) {
				if(!prime[i]) 
					continue;
				for(int j=i*i;j<=2*n;j+=i) {
					prime[j] = false;
				}
			}
			for(int i=n+1;i<=2*n;i++) {
				if(prime[i])
					result++;
			}
			System.out.println(result);
		}
	}
}