#include <fstream>

using namespace std;

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

#define MAXN 2000005

int n;
bool p[MAXN];

int main() {

    cin >> n;
    int ans = 0;

    for(int i = 3; i <= n; i+= 2)
    {
        if(p[i] == 0)
         ans++;

        for(int j = 2*i; j <= n; j += i)
         p[i] = 1;
    }

    cout << ans;
    return 0;
}