#include <fstream>

using namespace std;

const int Nmax = 2000005;

bool ciur[Nmax];

void build_ciur(int n){
    ciur[0] = 1;
    ciur[1] = 1;
    for(int i = 2; 1LL * i * i <= n; i++){
        if(ciur[i] == 0){
            for(long long j = i * i; j <= n; j += i){
                ciur[j] = 1;
            }
        }
    }
}

int count_primes(int n){
    int cnt = 0;
    for(int i = 2; i <= n; i++){
        if(ciur[i] == 0){
            cnt++;
        }
    }
    return cnt;
}

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

    int n;

    fin >> n;

    build_ciur(n);

    fout << count_primes(n);

    return 0;
}