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

    v[0]=1; v[1]=1;
    for (i=0;i<=n;i++)
        if(v[i]==0)
            nr++;
    g<<nr;
    return 0;
}