#include <stdio.h>
#include <math.h>

int prime(int n) 
{
	for (int i = 2; i <= sqrt((double)n); i++) 
	{
		if (n % i == 0) 
		{
			return 0;
		}
	}

	return 1;
}

int main() 
{
	int N;
	int count = 0;
     
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
 
    scanf("%d", &N);

	for (int i = 2; i < N; i++) 
	{
		if (prime(i)) 
		{
			count++;
		}
	}
    
    printf("%d\n", count);
	return 0;
}