#include<fstream>

using namespace std;

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

char a[2000001];
long n,nr;
int main(){
    int i,j;
        fin>>n;
        for(i = 2; i <= n; i++)
        if(a[i] == 0){
                nr++;
                for(j = i;j<= n; j+=i) 
                 a[j] = 1;
        }
    fout<<nr;
fin.close();
fout.close();
return 0;
}