#include <cmath>
#include <fstream>
#include <bitset>
using namespace std;
int n, rez;
bitset <2000001> v;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int main()
{
    cin >> n;
    v[0] = v[1] = 1;
    for(int i = 2; i <=n ; i++)
        if(!v[i])
        {
            for(int j = i;j <=n / i; j++)
                v[j * i]=1;
            rez++;
        }
    cout << rez;
    return 0;
}