リンク AOJ 0009 Prime Number
ソース
import java.util.*;
public class Main {
static Scanner sc = new Scanner(System.in);
static int[] prime;
static int n;
public static void main(String[] args) {
while(read()){
slove();
}
}
static boolean read(){
if(!sc.hasNextInt())
return false;
n = sc.nextInt();
return true;
}
static void Prime(int a){
prime = new int[a+1];
for(int i = 2; i < prime.length; i++)prime[i] = 1;
for(int i = 2; i < prime.length; i++){
if(prime[i] == 1){
for(int j = i*2; j < prime.length; j+= i)
prime[j] = 0;
}
}
}
static void slove(){
int res = 0;
Prime(n);
for(int i = 2; i < prime.length; i++){
if(prime[i] == 1)
res++;
}
System.out.println(res);
}
}