#include <iostream>
#include <fstream>
using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int n, i, j, c;
int fr[2000001];

int main()
{
    fin >> n;
    for(i = 2; i * i <= n; i++)
    {
       if(fr[i] == 0)
       {
           for(j = i * i; j <= n; j += i)
               fr[j] = 1;
       }
    }
    for(i = 2; i <= n; i++)
    {
        if(fr[i] == 0)
            c++;
    }
    fout << c;
    return 0;
}