#include <iostream>
#include <vector>

#define MAXN 2000000
using namespace std;

vector<int> prime(2000000, true);

void seive(int n){
    for(int i = 2; i<=n; i++){
        if(prime[i]){
            for(int j = i*i; j<=n; j+=i){
                prime[j] = false;
            }
        }
    }
}

int main(){
    ifstream fin("ciur.in"); ofstream fout("ciur.out");
    int n;
    fin >> n;
    seive(n);
    int k = 0;
    for(int i = 2; i<=n; i++){
        if(prime[i]) k++;;
    }
    cout << k << endl;
    fout << k << endl;
}