#include<fstream>
#include<math.h>
using namespace std;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    long i,j,cont=0,n;
    bool v[2000001];
    f>>n;

    for (i=0;i<n;++i)

        v[i]=0;
        v[0]=v[1]=1;

    for (i=4;i<=n;i+=2)
        v[i]=1;
    for (i=3;i<=sqrt(n);i=i+2)
        if (v[i]==0)
            for (j=i*2;j<=n;j=j+i)
                v[j]=1;

                for (i=2;i<=n;i++)

                    if(v[i]==0)
                    cont++;
                g<<cont;


}