#include<fstream>

using namespace std;

bool nb[2000001];

int main()
{
    int i,j,n,val = 0;

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

    in>>n;

    for(i = 2; i <= n; i++)
    {
        if(nb[i] != 1)
        {
            for(j = i + i; j <= n; j += i)
            {
                nb[j] = 1;
            }

            if(nb[i] == 0)
            {
                val++;
            }
        }
    }

    out<<val;

}