#include <fstream>
using namespace std;

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

int n;
bool e[2000001];

int main()
{
    e[0] = e[1] = 1;
    for (int i = 4; i <= 2000000; i += 2)
        e[i] = 1;
    for (int i = 3; i <= 1414; i += 2)
        if (e[i] == 0)
            for (int j = i * i; j <= 2000000; j += i)
                e[j] = 1;

    cin >> n;
    int cnt = 0;
    for (int i = 2; i <= n; ++i)
        if (!e[i])
            ++cnt;

    cout << cnt;
    return 0;
}