#include<iostream>
#include<cstdlib>
#include<algorithm>
#include<cstdio>
using namespace std;

//C

const int MAX_N = 1000000;
int prime[MAX_N];
bool is_prime[MAX_N + 1];

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) != EOF)
	{
		int ans = sieve(n);
		printf("%d\n", ans);
	}
}