#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    int n;
    fin >> n;
    vector<int> v(n + 1);
    for(int i = 2; i <= n; i++)
    {
        v[i] = 1;
    }
    int nrprime = 0;
    for(int i = 2; i <= n; i++)
    {
        if(v[i] == 1)
        {
            nrprime++;
            for(int j = 2 * i; j <= n; j += i)
            {
                v[j] = 0;
            }
        }
    }
    fout << nrprime;
    return 0;
}