#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[2000005];
int main()
{
    v[1]=1;
    int k=0;
    int n;
    fin>>n;
    for(int i=2;i<=n;i++)if(!v[i]){for(int j=i*2;j<=n;j+=i)v[j]=1;
                                    k++;}
    fout<<k;
    return 0;
}