#include <bits/stdc++.h>

using namespace std;

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

const int NMax =2e6 + 5;

int ans;
bitset < NMax > v;

inline void Ciur(const int &n){
    if(n > 2) ans++;
    for(int i = 3; i <= n; i += 2){
        if(!v[i]){
            ans++;
            for(long long  j =  i * i; j <= n; j += 2 * i){
                v[j] = true;
            }
        }
    }
}

int main(){
    int n;
    fin >> n;
    Ciur(n);
    fout << ans;
    return 0;
}