#include <fstream>
using namespace std;

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

int n,k,ok,i,j;

int main(){
    fin>>n;k=1;
    for (i=3;i<=n;i+=2){
        ok=1;
        for (j=3;j*j<=i && ok;j+=2)
            if (i%j==0)
                ok=0;
        k+=ok;
    }
    fout<<k;
    fin.close();
    fout.close();
    return 0;
}