#include<stdio.h>
int n,nr;
char prim[2000005];
int main(void)
{
	int i,j;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;++i)
		prim[i]=1;
	for(i=2;i<=n;++i)
		if(prim[i])
		{
			++nr;
			for(j=i+i;j<=n;j+=i)
				prim[j]=0;
		}
	printf("%d\n",nr);
	return 0;
}