#include<fstream>
#include<cmath>
using namespace std;
int main()
{
    ifstream in ("ciur.in");
    ofstream out ("ciur.out");
    int n,i,j,f,s;
    bool v[2000001]={0};
    in>>n;
    f=(int)sqrt((float)n);
    v[0]=v[1]=1;
    for (i=2;i<=f;++i)
            if (v[i]==0)
                    for (j=i*i;j<=n;j+=i)
                        v[j]=1;
    s=0;
    for (i=2;i<=n;++i)
            if (!v[i])
                ++s;
    out<<s;
    in.close();
    out.close();
    return 0;
}