#include <fstream>

using namespace std;

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

bool ciur[2000001];

int Eratostene(int N)
{
    long long i, j;
    int cnt = 1;

    ciur[1] = ciur[0] = 1;
    for (i = 4; i <= N; i += 2)
        ciur[i] = 1;
    for (i = 3; i * i <= N; i += 2)
        if (ciur[i] == 0)
            for (j = i * i; j <= N; j += 2 * i)
                ciur[j] = 1;
    for (i = 3; i <= N; i += 2)
        if (ciur[i] == 0)
            cnt++;
    return cnt;
}

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