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

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool prime[2000001];

int main(){
    int num;
    int prime_count = 0;
    fin >> num;
    for(int i = 2; i <= num; ++i){
        if(prime[i]){
            continue;
        }
        ++prime_count;
        for(int p = i * 2; p <= num; p += i){
            prime[p] = true;
        }
    }
    fout << prime_count;
}