#include <fstream>
#include <vector>
#include <iostream>
using namespace std;

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

unsigned int n;
vector<bool> ciur;

int main() {
    fin >> n;
    ciur = vector<bool>(n + 1, true);
    unsigned int counter = 0;
    for (unsigned int i = 2; i <= n; i++)
        if (ciur[i]) {
            counter++;
            for (unsigned j = i + i; j <= n; j += i)
                ciur[j] = false;
        }
    fout << counter;
    return 0;
}