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

printf("%d",nr);
}