#include<fstream>
using namespace std;
int p=0,n,i,j,c[100000001];
ifstream siin("ciur.in");
ofstream siout("ciur.out");   
int main()
{ 
     siin>>n;
     for (i = 2; i <= n; ++i) 
     {
         if (c[i] == 0)
           {
             p++;
            for (j = i + i; j <= n; j += i)
             {
                c[j] = 1;
}
}
}
     
    siout<<p;
    siout.close();
    siin.close();
    return 0;
}