#include <bits/stdc++.h>

using namespace std;

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

const int Nmax = 2e6 + 5;

int n;
bitset <Nmax> ciur;

int main()
{
    fin >> n;

    ciur[0] = ciur[1] = 1;

    int sol = 0;
    for(int i = 2; i * i <= n; i++)
        if(ciur[i] == 0)
            for(int j = i * i; j <= n; j += i)
                ciur[j] = 1;

    for(int i = 2; i <= n; i++)
        if(ciur[i] == 0) sol++;

    fout << sol << "\n";

    fin.close();
    fout.close();
    return 0;
}