#include <iostream>

#include <cmath>

using namespace std;

int main() {

int n;

int prime = 0;

int sum = 0;

int root;

while (1) {

sum = 0;

cin >> n;

if (n == 0) break;

else if (n == 1) cout << 1 << endl;

else {

for (int i = n + 1; i < 2 * n; i++) {

root = sqrt(i);

for (int j = 2; j <= root; j++) {

prime = 0;

if (i%j == 0) {

prime++;

break;

}

}

if (prime == 0) sum++;

}

cout << sum << endl;

}

}

}