#include <bits/stdc++.h>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int ciur [2000005];
int n;
int main ()
{
    fin >> n;
    int cnt = n - 1;
    for (int i = 2; i * i <= n; i++)
    {
        if (!ciur[i])
            for (int j = i; j <= n / i; j++)
                if (!ciur[j * i])
                {
                    ciur[i * j] = 1;
                    cnt--;
                }
    }
    fout << cnt;
}