#include <fstream>
#include <bitset>

#define MAXN 2000005

using namespace std;

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

bitset <MAXN> dp;

inline void Read() {
    int N, sol = 0;

    fin >> N;

    for (int i = 2; i <= N; i++) {
        if (!dp[i]) {
            for (int j = 2 * i; j <= N; j += i) {
                dp[j] = 1;
            }
            sol++;
        }
    }

    fout << sol << "\n";
}

int main () {
    Read();

    fin.close(); fout.close(); return 0;
}