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

using namespace std;

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

long long int frec[2000000];

int main()
{
    long long int n, cnt = 0;

    fin >> n;

    for(int i = 2; i <= n; i++){
        if (frec[i] == 0){
            cnt++;
            for(int j = i * 2; j <= n; j = j + i){
                frec[j] = 1;
            }
        }
    }

    fout << cnt;

    return 0;
}