#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int n, cnt = 0;
    bool prim[2000001];

    fin >> n;

    for (int i = 0; i <= n; i++)
        prim[i] = true;

    prim[0] = prim[1] = false;

    for (int i = 2; i * i <= n; i++)
        if (prim[i])
            for (int j = i * i; j <= n; j += i)
                prim[j] = false;

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

    fout << cnt;

    return 0;
}