#include <fstream>
using namespace std;
int n,i,j,sol;
char f[2000010];
int main () {
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin>>n;
    for (i=2;i<=n;i++){
        if (f[i]==0){
            for (j=i*2;j<=n;j+=i){
                f[j]=1;
            }
            sol++;
        }
    }
    fout<<sol;
    return 0;
}