#include <fstream>
#include <bitset>

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

bitset <2000007>a;
int n;

void Ciur(int x)
{
    int i, j, k;
    for (i=4; i<=x; i+=2)
        a[i]=1;
    for (i=3; i*i<=x; i+=2)
        if (a[i]==0)
            for (j=i*i; j<=n; j=j+2*i)
                a[i]=1;
    k=1;
    for (i=3; i<=x; i+=2)
        if (a[i]==0) k++;
    fout << k << "\n";
}

int main()
{
    fin >> n;
    Ciur(n);
    fin.close();
    fout.close();
    return 0;
}