#include <bits/stdc++.h>

using namespace std;

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

const int N_MAX = 2e6 + 5;

int N;
bitset < N_MAX > prime;

int cnt;


int main()
{
    fin >> N;
    for (int i = 2; i * i <= N; i += 1 + i % 2)
    {
        if (prime[i] == 0)
        {
            for (int j = i * i; j <= N; j += i)
                prime[j] = 1;
        }
    }
    for (int i = 2; i <= N; i++)
        cnt += 1 - prime[i];
    fout << cnt << "\n";
    return 0;
}