#include <fstream>
using namespace std;

int N, cnt;
char prim[2000005];

int main()
{
    int i, j;

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

    f >> N;

    for (i = 2; i <= N; ++i)
        if (!prim[i])
        {
            ++cnt;
            for (j = i*i; j <= N; j =j + i)
                prim[j] = 1;
        }

    g << cnt;

    return 0;
}