#include <iostream>
//#include <algorithm>
#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
short int v[2000003];
int main()
{
    f>>n;
    int i=2,nrprime=0;
    while(i<=n)
    {
        v[i]=1;
        nrprime++;
        int j=i*i;
        while(j<=n)
        {
            v[j]=-1;
            j+=i;
        }
        while(v[i]==1 or v[i]==-1)
            i++;
    }
    g<<nrprime;
    return 0;
}