#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
    int n,i,j,nr=0;
    in>>n;
    for(i=2;i<=n;i++)
    {
        for(j=2;j<=i/2;j++)
        {
            if(i%j==0)
            {
                v[i]=1;
                nr++;
                break;
            }

        }
    }

    out<<n-nr-1;
    return 0;
}