#include <fstream>
#include <vector>
using namespace std;

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

int n,k,i,j;
vector<bool> v;

int main(){
    fin>>n;
    for (i=0;i<=n+2;i++)
        v.push_back(true);
    for (i=2;i<=n;i++)
        if (v[i]){
            k++;
            for (j=2;j*i<=n;j++)
                v[j*i]=false;
        }
    fout<<k;
    fin.close();
    fout.close();
    return 0;
}