#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll nmax = 2000001;
bitset<nmax> reached;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int n;
    fin >> n;
    int cnt = 0;
    for (int i = 2; i <= n; i++)
    {
        if(!reached[i])
        {   cnt++;
            for (int j = i * i; j <= n; j += i)
                reached[j] = 1;
        }
    }

    fout << cnt;
}