#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 = 0;
    for (int i = 2;i <= n;i++)
    {
        if (!ciur[i])
        {
            for (int j = i * i;j <= n;j += i)
                ciur[j] = 1;
            cnt++;
        }
    }
    fout << cnt;
}