#include <fstream>
#include <cmath>
#define NMax 2000000
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int main()
{
    int sir[NMax];
    int aux=0,n;
    in>>n;
    for(int i=2;i<n;i++)
    {
        a[i]=1;
    }
    for (int i=2;i<sqrt(n);i++)
    {
        if(a[i])
            for (int j=i;i<n/i;j++);
        a[j*i]=0;
    }
    for (int i=2;i<n;i++)
    {
        if (a[i])
            aux++;
    }
    out<<aux;
    return 13;
}