#include <iostream>
using namespace std;

int main(void) {
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	int n,i,d=0,j;
	char v[n];
	
	cin >> n;
	
	for (i=2;i<=n;i++) 
	{
		v[i]=1;
	}
	i=2;
	
	while (i<=n) 
	{
		if (v[i])
		{
			d++;
			for (j=i;j<=n;j+=i) 
				v[j]=0;
		}
		i++;
	}
	cout << d;
}