#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
ifstream f("ciur.in", ios::in);
ofstream g("ciur.out", ios::out);

int ciur_eratostenes(int n) {
    int sol = 0, j;
    bitset<1> v[n + 1];
    for(int i = 2; i <= n; i++) {
        if(v[i] != 0) continue;

        sol++;
        for (j = i; j <= n ; j = j + i) {
            v[j] = 1;
        }
    }
    return sol;
}
int main() {
    int x;
    f>>x;
    g<<ciur_eratostenes(x);
    return 0;
}