#include <iostream>
#include <fstream>

using namespace std;
bool prime (int x){
    if (x==1)
        return false;
    if(x==0)
        return false;
    if(x==2)
        return true;
    for(int i=2;i*i<=x;i++)
        if(x%i==0 and x!=1 and x!=0 and x!=2)
            return 0;
    return 1;
}
int main()
{
    int N,c=0;
    ifstream f("ciur.in");
    ofstream g ("ciur.out");
    f>>N;
    for(int i=2;i<=N;i++)
        if(prime(i)==true)
            c++;
    g<<c;
    return 0;
}