#include <bits/stdc++.h>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
bool 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[i * j])
                        ciur[i * j] = 1, cnt--;
    fout << cnt;
}