#include <fstream>

using namespace std;

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

int n, cnt;
int prim[2000010];

int main(void)
{
    in >> n;

    for (int i = 2; i <= n; i++)
        if (prim[i] == 0)
        {
            cnt++;

            for (unsigned long long j = i * i; j <= n; j = j + i)
                prim[j] = 1;
        }

    out << cnt;

    return 0;
}