#include <fstream>
#include <bitset>
using namespace std;
bitset<2000002>a;
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, i, j, k;
    fin >> n;
    for (i=4; i<=n; i=i+2)
        a[i]=1;
    for (i=3; i*i<=n; i=i+2)
        if (a[i]==0)
            for (j=i*i; j<=n; j=j+2*i)
                a[j]=1;
    k=1;
    for(i=3; i<=n; i=i+2)
        if (a[i]==0)
        {
            k++;
        }
    fout << k<< "\n";
    fin.close();
    fout.close();
    return 0;
}