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