#include <cstdlib>
#include <fstream>

using namespace std;
char v[2000001];
int n,i,j,s;
int main(int argc, char *argv[])
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for(i=2;i<=n;i++) {
         if(v[j]==0) {
           s=s+1;          
           for(j=2*i;j<=n;j+=i) {
                   v[j]=1;
                }
         }                                               
    }
    
    g<<s;
    
    
    f.close();
    g.close();
    system("PAUSE");
    return EXIT_SUCCESS;
}