#include <iostream>
#include <fstream>
using namespace std;
bool a[2000001];

int ciur(int n)
{   int i=2, cont=0;
    while(i<=n)
    {
        if(a[i]==0)
         {   cont++;
             for(int j=2*i; j<=n; j+=i)
               a[j]=1;
             i++;
         }
        else i++;

    }
    return cont;
}

int main()
{   freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n;
    scanf("%d",&n);
    ciur(n);
    printf("%d",ciur(n));


    return 0;
}