#include <fstream>
#include <bitset>

using namespace std;

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

int n;
bitset<2000001> c;

int main()
{
    cin >> n;

    for(int i = 4; i <= n; i += 2)
        c[i] = 1;

    for(int i = 3; i * i <= n; i += 2)
        if(!c[i])
            for(int j = i * i; j <= n; j += 2 * i)
                c[j] = 1;

    int nrprime = 1;
    for(int i = 3; i <= n; i += 2)
        nrprime += !c[i];

    cout << nrprime;

    return 0;
}