#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*i<=n; ++i)
     if (viz[i]==0) {
                    ++sol;
                    for (j=i; i*j<=n; ++j) viz[i*j]=1;
                    }
    while (i<=n) { 
          if (viz[i]==0) ++sol;
          ++i;
          }
     fout<<sol;
 return(0);
}