#include <fstream>
using namespace std;
int n,i,j,p;
bool b[2000000];
ifstream fi("ciur.in");
ofstream fo("ciur.out");
int main()
{
    fi >> n;
    for(i=2;i<=n;i++){
      if(b[i] == false){
        p++;
        for(j=2*i;j<=n;j+=i) b[j] = true;
      }
    }
    /*
    for(i=2; i<=n; i++)
    {
        if(b[i] == false)
        {
            p++;
            b[i]=true;
            j=i;
            while(j<=n)
            {
                j+=i;
                if(b[j] != true) b[j] = true;
            }
        }
    }
    */
    fo << p;
    return 0;
}