#include <fstream>
#include <cmath>


using namespace std;

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, nr = 0;
    bool ciur[2000000];
    fin >> n;
    for (int i = 2; i <= n; ++i)
    ciur[i] = 1;
    for (int i = 2; i * i <= n; ++i)
        if (ciur[i])
            for (int j = i + i; j <= n; j = j + i)
                ciur[j] = 0;
    for (int i = 2; i <= n; ++i)
        if (ciur[i])
        ++nr;
    fout << nr;
    return 0;
}