#include <fstream>
#include <bitset>
#include <cmath>

using namespace std;
//double start,stop;
bitset <2000005> v;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int n;
    int i,j,nr=1;

    fin>>n;
    int limita=sqrt(n);


    for(i=4;i<=n;i+=2)
        v[i]=1;

    for(i=3;i<=limita;i+=2)
        if(v[i]==0)
        {
            nr++;
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
        }

    for(;i<=n;i+=2)
        if(v[i]==0)
        {
           nr++;
        }

    fout<<nr<<'\n';

    fin.close();
    fout.close();
    return 0;
}