#include<iostream>
#include<fstream>
using namespace std;
unsigned long n,nr=0;
char prim[2000005];
int main ()
{
    ifstream x("ciur.in");
    unsigned long i,j;
    ofstream y("ciur.out");
    x>>n;
    for(i=2;i<=n;i++)
        prim[i]=1;
        for(i=2;i<=n;i++)
        {
            if(prim[i])
            {
            nr++;
            for(j=i+1;j<=n;j+=i)
            prim[j]=0;
            }
        }
        y<<nr;
        x.close();
        y.close();
        return 0;
}