#include <cstdio>
#include <vector>
using namespace std;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, nr = 0; scanf("%d", &n);
    vector<bool> prim(n / 2 + 1);
    prim.assign(n, true);

    for (int i = 1; 2 * i * i + 2 * i <= n; i++)
        if (prim[i] == true)
        {
            nr++;
            for (int j = 2 * i * i + 2 * i; 2 * j + 1 <= n; j += 2 * i + 1)
                prim[j] = false;
        }

    printf("%d", nr);
    return 0;
}