#include<cstdio>
using namespace std;
int p[125100],n,nr;
int ciur(int n)
{
    int i,j,nr=1;
    for (i=1;((i*i)<<1)+(i<<1)<=n;i++)
        if ((p[i>>3] & (1<<(i&7)))==0)
                for (j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=((i<<1)+1))
                    p[j>>3]|=(1<<(j&7));
    for (i=1;2*i+1<=n;i++)
        if ((p[i>>3] & (1<<(i&7)))==0) nr++;
    return nr;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    nr=ciur(n);
    printf("%d",nr);
    return 0;
}