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