#include <fstream>

using namespace std;

bool ies[2000005];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n; f >> n;
    for(int i = 4; i <= n; i += 2) ies[i] = true;
    for(int i = 3; i <= n; i ++)
        if(!ies[i])
            for(int k = i * 2; k <= n; k += i)
                ies[k] = true;
    int nr = 0;
    for(int i = 2; i <= n; i ++) if(!ies[i]) nr ++;
    g << nr << "\n";
    return 0;
}