//Ciurul lui  Eratosthenes
#include <fstream>
using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
bool a[2000003];
int N,i,j,k;
int main() {
    fi>>N;
    a[0]=1;  //1 taiat (neprim)
    a[1]=1;   //0 prim
    for(i=2;i<=N;i++)
      if(a[i]==0)
          for(j=2*i;j<=N;j=j+i)a[j]=1;
    for(i=1;i<=N;i++)
       if(a[i]==0)k++;
    fo<<k;
    fi.close();fo.close();
    return 0;
}