#include <fstream>

using namespace std;

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

const int nmax=2000000;

bool v[nmax+1];

int main(){
    int n,sol=1;
    fin>>n;
    for(int i=3;i<=n;i+=2){
        if(v[i]==0&&i*i<=nmax){
            sol++;
            for(int j=i*i;j<=n;j+=2*i){
                v[j]=1;
            }
        }
    }
    fout<<sol<<"\n";
    return 0;
}