#include<fstream>
using namespace std;
int i,j,n,sol;
bool viz[2000005];

int main(void) {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    
    for (i=2; i<=n; ++i)
     if (viz[i]==0) {
                    ++sol;
                    for (j=2; i*j<=n; ++j) viz[i*j]=1;
                    }
     fout<<sol;
 return(0);
}