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