#include <iostream>
#include <fstream>

using namespace std;

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

int main() {
    int n, p=0;
    bool m[2000000];
    in>>n;
    for (int i=2; i<=n; i++) m[i] = true;
    for (int i=2; i<=n; i++) {
        if (m[i] == true) {
            for (int j=2*i; j<=n; j+=i) m[j] = false;
            //p++;
        }
    }
    for (int i=2; i<=n; i++) if (m[i] == true) p++;
    out<<p;
}