#include <fstream>
#include <bitset>
#include <vector>
#define NMAX 2000050

using namespace std;

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

bitset < NMAX > v;
int n;

int ciur()
{
    v[0] = v[1] = 1;
    int ans = 1;

    for (int i = 4; i <= n; i += 2)
        v[i] = 1;

    for (int i = 3; i <= n; i += 2)
        if (v[i] == 0)
        {
            ans ++;
            for (int j = 3 * i; j <= n; j += i)
                v[j] = 1;
        }
    return ans;
}

int main()
{
    f >> n;
    g << ciur() << '\n';
    return 0;
}