#include <fstream>
#define MAX 2000000
using namespace std;
int v[MAX];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,nr=1;
    f>>n;
    for(int i=3;i<=n;i+=2)
    {
        if(v[i]==0)
            {
                nr++;
                for(int j=i;j<=n;j+=i)
                    v[j] = 1;
            }

    }
    g<<nr;
}