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

ifstream in { "ciur.in" };
ofstream out { "ciur.out" };

#define N_MAX 2000005

bool not_prim[N_MAX];

int main() {
    int n; in >> n;
    
    for (int64_t i { 4 }; i <= n; i += 2)
        not_prim[i] = true;
    
    for (int64_t i { 3 }; i * i <= n; i += 2)
        if (!not_prim[i])
            for (int64_t j { 2 * i }; j <= n; j += i)
                not_prim[j] = true;
    
    int cnt { 0 };
    for (int i { 2 }; i <= n; ++i)
        cnt += !not_prim[i];
    
    out << cnt;
}