#include <iostream>
#include <fstream>

using namespace std;

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

int n,nr;
bool prim[2000005];

int main()
{
    cin>>n;
    for(int i=2;i*i<=n;i++)
    {
        if(prim[i]==0)
        {
            nr++;
            for(int j=i+1;j<=n;j+=i)
                prim[i]==1;
        }
    }
    cout<<nr;
    return 0;
}