#include <fstream>
#include <cmath>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool a[2000002];
int main()
{
    int n,i,ok=0,j;
    in>>n;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            ok++;
            for(j=i;j<=n;j=j+i)
                a[j]=1;
        }
    }
    out<<ok;
    return 0;
}