#include <bits/stdc++.h>

using namespace std;

bool ciur[2000005];
int nr,n;

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    in>>n;
    for (int i = 2; i * i <= n;++i)
          if (ciur[i] == false)
               for (int j = i * i;j <= n;j += i)
                    ciur[j] = true;
    for (int i = 2;i <= n;++i)
         nr += (ciur[i] == false);
    out<<nr;
    return 0;
}