#include <fstream>

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

int k;
bool a[2000005];
void Ciur(int c)
{
    int i,j;
    for(i=3;i*i<=c;i+=2)
        if(a[i]==false)
            for(j=i*i;j<=c;j+=2*i)
                a[j] = true;
    k = 1;
    for(i=3;i<=c;i+=2)
        if(a[i]==false)
            k++;

      fout<<k<<"\n";
}

int main()
{
    int n;
    fin>>n;
    Ciur(n);
    fout.close();
    return 0;
}