#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[2000001];
int main()
{
    long n;
    fin>>n;
    int i,c=1;
    v[1]=1;
    for(i=3;i<=n;i+=2)
    {
       if(v[i]==0)
       {
           c++;
           for(int j=2*i;j<=n;j+=i)
            v[j]=1;
       }
    }
    fout<<c;
    return 0;
}