#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
bool v[2000000];
void Eratostene()
{
   int i,j;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            for(j=i+i;j<=n;j+=i)
                v[j]=1;
        }
    }
}
void read_number_and_process()
{
    f>>n;
    Eratostene();
    int i,counter=0;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
            counter++;
    }
    g<<counter<<"\n";
}
int main()
{
    read_number_and_process();
}