#include <fstream>
#include <cmath>

using namespace std;

bool    prim[2000002];
int     n, rs;

ifstream cin ("ciur.in");
ofstream cout("ciur.out");

int main() {
    
    cin >> n;
    rs = n - 1;
    int p = (int)sqrt(n);
    
    for(int i = 2; i <= p; i++)
        if(!prim[i])
            for(int j = 2; i * j <= n; j++) rs -= int(prim[i*j] == 0), prim[i*j] = 1;
    
    cout << rs;
    
    return 0;
}