#include "bits/stdc++.h"
using namespace std;
ifstream in;
ofstream out;
int main(){
in.open("ciur.in");
out.open("ciur.out");
    int n;
    in>>n;
    int k = 0;
    bool prime[n+1];
    memset(prime, true, n+1);
    prime[0] = false; prime[1] = false;
    for(int p = 2; p<=sqrt(n); p++){
        if(prime[p]){
            for(int i = p+p; i<=n; i+=p){
                prime[i] = false;
            }
        }
    }
    for(int i = 0; i<=n; i++){
        if(prime[i]) k++;
    }
    out<<k;
}