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

    for(int i = 2; i <= n ; i++)
        if(!p[i])
            ans++;
        
        cout << ans;
    return 0;
}