#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
bitset <2000001> v;

int main()
{
    int n, k=0;
    f >> n;
    v[0]=v[1]=1;
    for (int i = 1 ; i <= 2000000 ; ++i)
    {
        if (v[i] == 0)
        {
            for (int j = i * 2 ; j <= 2000000 ; j += i)
                v[j]=1;
        }
    }
    for (int i = 1 ; i <= n ; ++i)
    {
        if(v[i] != 1) k++;
    }
    g << k;
    return 0;
}