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

unsigned int a[2000000];

int main()
{
    unsigned int s=1,n;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;

    for(int i=3;i<=n/2;i+=2)
        if(a[i]==0)
            {s++;
            for(int j=i;j<=n/2;j+=i) a[i]=1;}

    g<<s;

    f.close();
    g.close();
    return 0;
}