#include <fstream>
#include <iostream>
#include <cmath>

using namespace std;

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

const int NMax = 2e6 + 5;

int N;
bool notPrime[NMax];

int ciur(int);

int main() {
    in>>N;
    out<<ciur(N);
    in.close();out.close();
    return 0;
}

int ciur(int x) {
    int ans = 1;

    for (int i=3;i<=x;i+=2) {
        if (!notPrime[i]) {
            ++ans;
            for (int j=3*i;j<=x;j+=2*i) {
                notPrime[j] = true;
            }
        }
    }
    return ans;
}