#include<fstream>
#include<cmath>
using namespace std;
ifstream fin("date.in");
ofstream fout("date.out");
int n,d,i,sol,nr,j,r;
int main(){
    fin>>n;
    for(i=2;i<=n;i++){
        j=2;
        nr=0;
        r=sqrt(i*1.0);
        while(j<=r){
            if(i%j==0){
                nr=1;
                break;
            }
            j++;
        }
        if(nr==0){
            sol++;
        }
    }
    fout<<sol;
    return 0;
}