#include<stdio.h>
#include<bitset>

using namespace std;

bitset<2000010> v;

int main()
{
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	int n, count = 0;

	scanf("%d", &n); 

	for(int i = 2 ; i < n ; ++i)
		if(!v[i]) {
			++count;

			for(int j = i ; j < n ; j += i)
				v[j] = 1;
		}

	printf("%d", count);

	return 0;
}