#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>



bool isPrime(int n)
{
	for (int i = 2; i * i <= n; i++)
	{
		if (n % i == 0)
			return 0;
	}
	return 1;
}
bool viz[2000000];
int main()
{
	int n;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);

	int num=0;
	for (int i = 2; i <= n; i++)
	{
		if (!viz[i])
		{
			num++;
			for (int j = i; j <= n; j += i)
				viz[j] = 1;
		}
	}
	printf("%d", num);
}