#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
#define ll long long

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

int n;
bool isPrime[2000001];
int main()
{
    fin >> n;
    fill(isPrime, isPrime + n + 1, true);
    for (int i = 2; i <= n; ++i)
    {
        if (isPrime[i])
        {
            for (int j = 2; j * i <= n; ++j)
            {
                isPrime[j * i] = false;
            }
        }
    }
    int cnt = 0;
    for (int i = n; i > 1; --i)
    {
        cnt += isPrime[i];
    }
    fout << cnt;
    return 0;
}