#include <fstream>
#include <vector>

using namespace std;

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

const int NMAX = 2000000;

int N;
bool d[NMAX + 5];
vector <int> primes;

void Init()
{
    for(int i = 3; i * i <= NMAX; i += 2)
        if(d[i] == 0)
            for(int j = i * i; j <= NMAX; j += 2 * i)
                d[j] = 1;
}

int main()
{
    Init();

    fin >> N;

    if(N >= 2)
        primes.push_back(2);

    for(int i = 3; i <= N; i += 2)
        if(d[i] == 0)
            primes.push_back(i);

    fout << primes.size() << '\n';

    return 0;
}