#include <bits/stdc++.h>
using namespace std;

string problem = "ciur";
ifstream fin (problem + ".in");
ofstream fout(problem + ".out");

// https://www.infoarena.ro/problema/ciur

int n,nr = 0;
bool numere[2000005];

int main()
{
    fin >> n;
    for (int i = 2; i <= n; i++)
        if(numere[i] == false)
        {
            nr++;
            for (int j = i + i; j <= n; j+=i)
                numere[j] = true;
        }
    fout << nr;
}