#include<cstdio>
using namespace std;
int a[2000001];
int main()
{
	int n,i,j,contor;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d ",&n);
	contor=0;
	for(i=4;i<=n;i+=2)
		a[i]=1;
	for(i=3;i*i<=n;i+=2)
		if(a[i]==0)
			for(j=i*i;j<=n;j=j+2*i)
				a[j]=1;
	for(i=2;i<=n;i++)
		if(a[i]==0)
			contor++;
	printf("%d ",contor);			
	return 0;
}