#include <iostream>
#include <cmath>
#include <fstream>
using namespace std;
ofstream out;
ifstream in;
bool c[2000000];
int main(){
    in.open("ciur.in");
    out.open("ciur.out");
    int n,s=0; in>>n;
    for(int i=2; i<=n; ++i){
        if(c[i]==0) ++s;
        for(int j=i+i; j<=n; j+=i){
            ++c[j];
        }
    }
    out<<s;
    return 0;
}