#include <bits/stdc++.h>

using namespace std;

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

bitset<2000005> ciur;
int n;

void Ciur(int n)
{
    ciur[0] = ciur[1] = 1;
    for (int i = 4; i <= n; i += 2) ciur[i] = 1;
    for (int i = 3; i * i <= n; i += 2)
        if (!ciur[i])
            for (int j = i * i; j <= n; j = j + 2 * i) ciur[j] = 1;
}

int main()
{

    int i, cnt = 0;
    fin >> n;
    Ciur(n + 1);
    for (i = 1; i <= n; i++)
        if (!ciur[i]) cnt++;
    fout << cnt << "\n";
    fin.close();
    fout.close();

    return 0;
}