#include<stdio.h>
using namespace std;
bool je[2000020];
long long i,j,n,nr;
int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n);
for(i=2;i<=n;i++)
	if(je[i]==0)
	{
		if(i*i<=n)
		{
			for(j=1LL*i*i;j<=n;j=j+i)
				je[j]=1;
		}
		nr++;
	}
printf("%d\n",nr);
return 0;
}