#include<stdio.h>
int n,i,j,q,z,a[1000000];
bool p[100000000];
int main ()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	p[1]=1;
    p[2]=0;
    q=1;
    a[1]=2;
    for(i=3;i<=n;i+=2)
    {
        if(p[i]==0)
        {
            q++;
            a[q]=i;
            if(z==0)
            {
                for(j=i*i;j<=n;j+=i)
                {
                    p[j]=1;
                }
                if((i+2)*(i+2)>n)z=1;
            }
        }
    }
    printf("%d\n",q);
	//for(i=1;i<=q;i++)
    //    printf("%d,",a[i]);
	return 0;
}