#include <iostream>
#include <fstream>
#include <cassert>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bool prim[2000005];
int n;
int main()
{
    f >> n;
    int nr = 0;
    fill(prim+1,prim+n+1,true);
    for (long long i = 2;i <= n;i++)
    {
        if (prim[i])
        {
            for (long long j = i * i;j <= n;j += i)
                prim[j] = false;
            nr++;
        }
    }
    g << nr;
    f.close();
    g.close();
    return 0;
}