#include <fstream>
using namespace std;
int i,n,x[2000003],c,j;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for(i=2;i<=n;i++)
        x[i]=1;
    for(i=2;i<=n;i++)
    {
        if(x[i])
            c++;
        for(j=i+i;j<=n;j=j+i)
            x[i]=0;
    }
    fout<<c;
    fout.close();
    return 0;

}