#include <fstream>

using namespace std;
bool v[2000001];
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int main()
{
    int n,s=0,k=0,i=2;
    cin>>n;
    while(i<=n)
    {
        if(!v[i])
        {k=0;

        s++;
            while(i*k<=n)
            {
                v[i*k]=true;
                k++;
            }
        }i++;
    }cout<<s;
    return 0;
}