#include <iostream>
#include <fstream>
using namespace std;
bool ciur[2000001];
int main()
{
    int i,j,n,nr=0;
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
    for (i=2;i*i<=n;i++)
    if (!ciur[i])
    for (j=2;j*i<=n;j++)
    ciur[j*i]=1;
    for (i=2;i*i<=n;i++)
    if (!ciur[i])
    ++nr;
    out<<nr;
    in.close();
    out.close();
    return 0;
}