#include <cstdio>
#include <cmath>

using namespace std;

const int N = 6000005;

bool sir[N];
int n;
int nr = 0;

void citire()
{
	scanf("%d", &n);
}

void solve()
{
	int lim = n;
		
	for(int i = 2; i <= lim; i++)
	{
		if(sir[i] == true)
		{
			continue;
		}

		nr++;
			
		for(int j = i * i; j <= n; j += i)
		{
			sir[j] = true;
		}
	}

	printf("%d", nr);
}

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

	citire();
	solve();

	return 0;
}