#include<fstream>
using namespace std;
int v[2000001],n,i,j,k=1;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for(i=1;((i*i)<<1)+(i<<1)<=n;++i)
        if(!(v[i>>5]&(1<<(i&31))))
            for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
                v[j>>5]|=(1<<(j&31));
    for(i=1;2*i+1<=n;++i)
        if(!(v[i>>5]&(1<<(i&31))))
            k++;
    g<<k;
}