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

int nrPrime;
bool nuEPrim[2000005];

void Ciur(int n)
{
    nuEPrim[0] = true;
    nuEPrim[1] = true;
    for (int i = 4; i <= n; i += 2)
    {
        nuEPrim[i] = true;
    }
    for (int i = 3; i <= n; i += 2)
    {
        if (nuEPrim[i] == false)
        {
            for (int j = 2 * i; j <= n; j = j + i)
            {
                nuEPrim[j] = true;
            }
        }

    }
}

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

    scanf("%i", &n);
    Ciur(n);

    for (int i = 2; i <= n; i++)
    {
        if (nuEPrim[i] == false)
        {
            nrPrime++;
        }
    }
    printf("%i", nrPrime);

    return 0;
}