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

using namespace std;

bitset<2000002> p;

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

    int n;
    cin>>n;
    p.set();
    p[0] = p[1] = false;
    int l = sqrt(n*1.0);
    for(int i = 2; i <= l; i++)
        if(p[i])
        {
            for(int j = i * i; j <= n; j += i)
                p[j] = false;
        }
    int sol = 0;
    for(int i = 1; i <= n; i++)
        sol += p[i];
    cout<<sol;

    return 0;
}