#include <fstream>
#include <bitset>
 using namespace std;
 bitset <2000001>a;
int main()
{
    int i,j,n,k;


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

    fin>>n;

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

    for(i=3;i*i<=n; i=i+2)
        if(a[i]==0)
            for(j=i*i;j<=n;j=j+2*i)a[j]=1;
    k=1;

    for(i=3; i<=n; i=i+2)
            if(a[i]==0)k++;

    fout<<k;

    fin.close();
    fout.close();

    return 0;
}