#include <iostream>
#include <fstream>
#define nmax 2000005
using namespace std;

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

int ciur(int n) {
    int i, j, cnt = 0;
    bool A[nmax];
    for (i = 2; i <= n; i++)
        if (!A[i]) {
            cnt++;
            for (j = 2 * i; j <= n; j += i)
                A[j] = 1;
        }
    return cnt;
}

int main() {
    int n;
    fin >> n;
    fout << ciur(n) << "\n";
    fin.close();
    fout.close();
    return 0;
}