#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int a[2000000];
int main()
{
    int n,i,j,x;
    f>>n;

    for(i=2;i<=n;i++)
        a[i]=1;
    for (i=1;i<=n;i++)
        if(a[i])
         {
             x++;
             for (j=i*2;j<=n;j+=i)
                 a[j]=0;
         }
         g<<x<<"\n";
    return 0;
}