#include<stdio.h>
//int n,i,j,q,z,a[1000000];
//bool p[100000000];
int n,i,j,nr;
char p[6250001];
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]);*/
    nr=1;
    for (i=1;((i*i)<<1)+(i<<1)<=n;i+=1)
    {
        if ((p[i >> 3] & (1 << (i & 7))) == 0)
        {
            nr++;
            for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1)
            {
                p[j >> 3] |= (1 << (j & 7));
            }
        }
    }
    j=i;
    for (i = j; 2 * i + 1 <= n; ++i)
         if ((p[i >> 3] & (1 << (i & 7))) == 0)
             nr++;
    printf("%d",nr);
	return 0;
}