#include <iostream>
#include <math.h>
#include <fstream>
using namespace std;
char a[2000005],i,g,n,s;
int main()
{
    ifstream ka("ciur.in");
    ofstream ki("ciur.out");
    ka>>n;
    for(g=2;g<=n;g=g+2)
    a[g]=1;
    s=1;
    for(i=3;i<=sqrt(n);i=i+2)
    {
        if(a[i]==0)
        {
            s++;
            for(g=i;g<=n;g=g+i)
            a[g]=1;
        }
    }
    for(i=i;i<=n;i=i+2)
    {
        if(a[i]==0)
        s++;
    }
    ki<<s;
}