#include <fstream>
#define nmax 2000005
using namespace std;

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

bool prim[nmax];

int main()
{
    unsigned n, i, j, k = 0;
    fin >> n;
    for (i = 2; i <= n; ++i)
        prim[i] = 1;
    for (i = 2; i <= n; ++i)
        if (prim[i]){
            ++k;
            for (j = 2 * i; j <= n; j += i)
                prim[j] = 0;
        }
    fout << k << '\n';
    fin.close();
    fout.close();
    return 0;
}