[백준]4948-베르트랑 공준(설명X)

//#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
//#include <iostream>
//using namespace std;
 
int main()
{
    int min;
    //cin >> min >> max;
    scanf("%d", &min);
    while (min != 0) {
        bool* ary = new bool[min * 2 + 1]{ false };
        ary[1] = true;
        int num = 0;
        for (int i = 2; i <= min; i++)
            if (!ary[i])
                for (int j = 2; j * i <= min * 2; j++)
                    ary[i * j] = true;
 
        for (int i = min + 1; i <= min * 2; i++)
            if (!ary[i])
                num++;
        //cout << i << endl;
        printf("%d\n", num);
        delete[] ary;
        scanf("%d", &min);
    }
}