#include <iostream>
#include <bits/stdc++.h>

using namespace std;

int a[2000000];

int main()
{
    ifstream cin ("ciur.in");
    ofstream cout ("ciur.out");
    int n;
    cin >> n;
    for (int i = 2; i < n; i++)
        if (a[i] == 0)
            for (int j = i+i; j < n; j += i)
                a[j] = 1;
    int c = 0;
    for (int i = 2; i < n; i++)
        if (a[i] == 0)
            c++;
    cout << c;
    return 0;
}