#include<fstream>
#include<cmath>
using namespace std;

bool a[10000002];

int main(void){
    ifstream fin("ciurul.in");
    ofstream fout("ciurul.out");
    int i,j,n,k,nr=0; 
    fin>>n; fin.close(); k=int(sqrt(n));
    for(i=2;i<=k;++i)
      if(!a[i])for(j=2;j<=n/i;++j)a[i*j]=1; 
    for(i=2;i<=n;++i)if(!a[i])++nr; fout<<nr;                                      
    fout.close();    
 return 0;   
}