#include <bits/stdc++.h>

using namespace std;

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

const int NMAX = 2e6 + 1;

int main()
{
    int n, cntPrime = 0;
    bool isPrime[NMAX];
    fin >> n;

    for(int i = 2; i <= n; i++)
    {
        isPrime[i] = true;
    }

    for(int i = 2; i <= n; i++)
    {
        if(isPrime[i])
        {
            for(int j = i * 2; j <= n; j += i)
            {
                isPrime[j] = false;
            }
        }
    }

    for(int i = 2; i <= n; i++)
    {
        if(isPrime[i])
        {
            cntPrime++;
        }
    }

    fout << cntPrime;

    return 0;
}