#include <fstream>
#include <string.h>

using namespace std;
const int Nmax = 2000005;

char P[Nmax];

int main()
{
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
    int N;
    f >> N;

    memset(P, 1, (N+1)*sizeof(char));
    P[0] = P[1] = 0;

    for (int i = 2; i*i <= N; i++)
        if (P[i])
            for (int j = i*i; j <= N; j += i)
                P[j] = 0;

    int answer = 0;
    for (int i = 2; i <= N; i++)
        if (P[i]) answer++;

    g << answer << endl;

    return 0;
}