#include <fstream>
#include <vector>
using namespace std;
vector<bool> a(2000002);
//vector<int>prim;
int sol,n;

int main()
{int i,j;
ifstream in("ciur.in");
in>>n;
in.close();
i=2;
while(i<n)
    {
        while(a[i]&&i<n)i++;
		if(a[i])break;
        sol++;
      //  prim.push_back(i);
        j=1;
        while(i*j<=n){a[i*j]=1;j++;}
    }

ofstream out("ciur.out");
//for(i=0;i<prim.size();i++)out<<prim[i]<<' ';out<<'\n';
out<<sol<<'\n';
out.close();
return 0;    
}