#include <fstream>
#include <bitset>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
const int NMAX = 2e6;
bitset <NMAX + 3> f;
int main()
{
    int n, i, j;
    cin >> n;
    if (n == 2)
        cout << 0;
    else
        for (i = 3; i * i <= n; i += 2)
            if (f[i] == 0)
                for (j = i * i; j <= n; j += 2 * i)
                    f[j] = 1;
    int cnt = 1;
    for (i = 3; i <= n; i += 2)
        cnt += !f[i];
    cout << cnt;
}