#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N,nrp,i,j;bool v[2000005];

int main()
{
    fin>>N;
    nrp=1;
    for(i=1;i<=(N-1)/2;++i)v[i]=1;
    for(i=1;i<=(N-1)/2;++i)
    {
        if(v[i]==1)
        {
            ++nrp;
            for(j=2*i*(i+1);j+2*i+1<=N;j+=2*i+1)v[j]=0;
        }
    }
    fout<<nrp;

    return 0;
}