#include <fstream>
#include <bitset>
#define nmax 2000002
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset <nmax> v;

int main()
{
    int n;
    fin>>n;
    for(int i=3;i<=n;i+=2)
        if(v[i]==0)
            for(int j=3;i*j<=n;j++)
                v[i*j]=1;
    int cont=1;
    for(int i=3;i<=n;i+=2)
        if(!v[i])
            cont++;
    fout<<cont;
    return 0;
}