#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int ciur[2000001];
int main()
{
    int n,nr = 0;
    in>>n;
    for (int i = 2; i * i <= n; ++i)
    {
        if (!ciur[i])
            for (int j = i * i; j <= n; j += i)
                ciur[j] = true;
    }
    for (int i = 2;i <= n;++i)
         if (!ciur[i])
             ++nr;
    out<<nr;
    return 0;
}