#include <stdio.h>
#include <iostream>
using namespace std;

#define MAXSIZE 2000001

char p[MAXSIZE];

int Primes_1(int n)
{
    int i, j, nr = 0;
    for (i = 2; i <= n; ++i)
        if (p[i] == 0)
        {
            nr++;
            for (j = 2*i; j <= n; j += i)
            p[j] = 1;
        }
    return nr;
}

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    int N;
    cin >> N;
    cout << Primes_1(N) << '\n';

    return 0;
}