#include <iostream>
#include <fstream>
using namespace std;
int main () {
ifstream in("ciur.in");
ofstream out("ciur.out");
 bool estePrim[2000000];
 int i,x,n,a,j,contor=0;
 in>>n;
 for(i=1;i<n;i++) estePrim[i] = true;
 for (x=2;x<n;x++)
 { if( estePrim[x] == true )
        { for(j = 2 * x  ; j < n ; j = j + x) estePrim[j] = false;
        contor++;
        }
}

out<<contor;
}