#include <iostream>
#include <string>
#include <vector>

#include <math.h>

using namespace std;

static inline bool judge_prime(const int num) {
	if (num < 2) {
		return false;
	}
	else if (num == 2) {
		return true;
	}
	else if (num % 2 == 0) {
		return false;
	}
	else if (num == 3) {
		return true;
	}

	if (num % 3 == 0) {
		return false;
	}

	if(num % 6 != 1 && num % 6 != 5) {
		return false;
	}

	const double sqrtnum = sqrt(num);
	for(int i = 5; i <= sqrtnum; i += 6) {
		if(num % i == 0) {
			return false;
		}
		if (num % (i + 2) == 0) {
			return false;
		}
	}
	return true;
}

static int count_prime(const int input) {
	int counter_prime = 0;

	for (int i = input; 1 < i; i --) {
		if (judge_prime(i)) {
			counter_prime ++;
		}
	}
	return counter_prime;
}

int main() {
	int input;
	while(cin >> input) {
		cout << count_prime(input) << endl;
	}
	return 0;
}

