#include <iostream>
#include <fstream>
using namespace std;
int n,v[2000005],c;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    in>>n;
    for (int i=2;i<=n;i++) v[i]=1;
    for (int i=2;i<=n;i++)
        if(v[i])
        {
            c++;
            for (int j=i+i;j<=n;j+=i)
                v[j]=0;
        }
    out<<c;
    return 0;
}