#include<cstdio>
using namespace std;
bool uz[2000005];
int nr, n;

int ciur(int n)
{
	for(int i=2;i<=n;++i)
		if(!uz[i])
		{
		++nr;
		for(int j=i+i;j<=n;j+=i)
			uz[j]=1;
		}
	return nr;
}
	
int main()
	{
		freopen("ciur.in","r",stdin);
		freopen("ciur.out","w",stdout);
		
		scanf("%d", &n);
		
		printf("%d\n", ciur(n));
		
		return 0;
}