#include <fstream>

using namespace std;

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

int ciur[2000001];

int Eratostene(int N)
{
    int i, j, cnt = 0;

    ciur[1] = ciur[0] = 1;
    for (i = 2; i <= N; ++i)
        if (ciur[i] == 0)
        {
            cnt++;
            for (j = 2 * i; j <= N; j += i)
                ciur[j] = 1;
        }
    return cnt;
}

int main()
{
    int N;
    in >> N;
    in.close();
    out << Eratostene(N) << '\n';
    out.close();
    return 0;
}