#include <fstream>
#include <bitset>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

const int N = 2e6 + 6;
bitset<N>ciur;

int main()
{
    int n, ans;

    in >> n;

    ans = 2;

    for(int i = 5; i <= n; i += 6)
    {
        if(ciur[i] == 0)
        {
            ans++;
            for(int j = i * i; j <= n; j += 2 * i)
                ciur[j] = 1;
        }
        if(ciur[i + 2] == 0)
        {
            ans++;
            int nr = i + 2;
            for(int j = nr * nr; j <= n; j += 2*nr)
                ciur[j] = 1;
        }
    }

    if(n == 2) out << 1;
    else if(n < 5) out << 2;
    else out << ans;

    return 0;
}