#include<stdio.h>
int n,ciur[2000000], nr=0,i,j;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;++i)
		if(ciur[i]==0) 
		{
			nr++;
			ciur[i]=1;
			for(j=i*2;j<=n;j=j+i)
				ciur[j]=1;
		}
	printf("%d",nr);		
	return 0;
}