#include <fstream>
#include <vector>

using namespace std;

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

vector<bool> a;

int main()
{
    int n;
    fin >> n;
    a.resize(n);
    for(int i = 2; i * i <= n; i++)
        for(int j = i; j <= n / i; j++)
            a[i * j] = true;
    int c = 0;
    for(int i = 2; i <= n; i++)
        if(a[i] == false)
            c++;
    fout << c;
    return 0;
}