#include<fstream>
using namespace std;
int p=0,n,i,j;
char c[2000001];
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;
}