#include <fstream>
using namespace std;
char fr[2000005];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,q;
    fin>>n;
    for(int i=3;i<=2000000;i+=2)
    {
        if(fr[i]==0)
        {
            for(int j=3*i;j<=2000000;j+=i)
              fr[j]=1;
        }
    }
    q=1;
    for(int i=3;i<=n;i+=2)
    {
        if(fr[i]==0)
        {
            q++;
        }
    }
    fout<<q;
    return 0;
}