#include <iostream>
#include <fstream>
#define dMAX 2000001

using namespace std;

int counter, N;
bool prime[dMAX];
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int i, j;
    fin >> N;
    prime[1] = true;
    for (i = 2; i <= N; i++) {
        if (!prime[i]) {
            counter++;
            for (j = i + i; j <= N; j += i) {
                prime[j] = true;
            }
        }
    }

    fout << counter;

    return 0;
}