#include<iostream>
#include<stdio.h>
using namespace std;
int prime[1000000];
bool is_prime[1000000];
int sieve(int n) {
	int p = 0;
	for (int i = 0;i <= n;i++) {
		is_prime[i] = true;
	}
	is_prime[0] = is_prime[1] = false;
	for (int i = 2;i <= n;i++) {
		if (is_prime[i]) {
			prime[p++] = i;
			for (int j = 2 * i;j <= n;j += i)is_prime[j] = false;
		}
	}
	return p;
}
int main()
{
	int n;
	while (scanf("%d",&n)) {
		printf("%d\n", sieve(n));
	}
			
	

    return 0;
}