#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, nr, p[2000001];
int main()
{
    fin >> n;
    for(int i = 2; i <= n; i++)
        if(!p[i])
        {
            nr++;
            for(int j = i + i; j <= n; j += i)
                p[j] = 1;
        }
    fout << nr;
}