#include <fstream>
#include <bitset>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
bitset <20000002> viz;
int n;
int main()
{
    fin>>n;
    int c=1;
    for (int i=3;i<=n;i+=2)
        if (viz[i]==0)
        {
            if (i*i<=n)
            for (int j=i*i;j<=n;j+=i)
                viz[j]=1;
        }
    for (int i=3;i<=n;i+=2)
        if (viz[i]==0)
            c++;
    fout<<c;
    return 0;
}