#include<cstdio>
bool f[2000001];




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