#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,j;
    in>>n;
    for(int i=2;i<n;i++)
    {
        sir[i]=1;
    }
    for (int i=2;i<sqrt(n);i++)
    {
        if(sir[i])
        for (j=i;j<n/i;j++);
        sir[j*i]=0;
    }
    for (int i=2;i<n;i++)
    {
        if (sir[i])
            aux++;
    }
    out<<aux;
    return 13;
}