#include <fstream>
#include <cmath>
#define NMax 2000000
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

bool sir[NMax];
int n;

int main()
{

    int aux=0;

    in>>n;

    for(int i=2;i<n;i++)
    {
        sir[i]=1;
    }
    for (int i=2;i<n;i++)
    {
        if(sir[i])
        for (int j=i+i; j<n;j = j + i)
            sir[j]=0;
    }
    for (int i=2;i<n;i++)
    {
        if (sir[i])
            aux++;
    }
    out<<aux;
    return 0;
}