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


int prim(int a) {int k=0;
if((a%2==0)&&(a>2))
return 0;
    for(int i=3;i<a/2;i++)
        if(a%i==0)
        return 0;
        return 1;
}
int main()
{ifstream f("ciur.in");
ofstream g("ciur.out");
int N,k=0;
f>>N;
for(int i=2;i<=N;i++)
    if(prim(i))
        k++;
    g<<k;
    return 0;}