prime_number

#include <stdio.h>

int main() {
    int arr[246913] ={0,};
    for (int i = 2; i <= 123456; i++){
        for (int j = 2; j*i <= 246912; j++ ) {
            arr[j*i] =  1;
        }
    }
    while (1) {
        int n, cnt = 0; scanf("%d",&n);
        if(n <= 0) break;
        
        for (int i = n+1; i <= 2*n; i++) 
            if (arr[i] == 0) cnt++;
        printf("%d\n",cnt);
    }
    return 0;
}