#include<stdio.h>
int n,i,j,nr;
bool k[2000013];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;++i)k[i]=1;
	i=2;
	nr=0;
	while(i*i<=n)
	{
		if(k[i])
		{
			j=i;
			while(i*j<=n)
			{
				k[i*j]=0;
				++j;
			}
		}
		++i;
	}
	for(i=2;i<=n;++i)if(k[i])++nr;
	printf("%d",nr);
	return 0;
}