using namespace std;
#include <fstream>
 
int n, nr;
char prim[2000010];
 
int main()
{
    int i, j;
     
    ifstream f("ciur.in");
    ofstream g("ciur.out");
 
    f>>n;
    for (i = 2; i <= n; ++i)
        prim[i] = 1;
    for (i = 2; i <= n; ++i)
        if (prim[i])
        {
            nr++;
            for (j=2*i;j<=n;j=j+i)
                prim[j] = 0;
        }
 
    g<<nr;
 
    return 0;
}