#include <fstream>
#include <bitset>

using namespace std;

bitset <2000001>a;

int main()
{
    int i, j, n,k;


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

    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;

    fin.close();
    fout.close();

    return 0;
}