// https://goo.gl/fBmFxu
#include <bits/stdc++.h>
using namespace std;

#define NMAX        2000000
#define MMAX        200009
#define kInf        (1 << 30)
#define kInfLL      (1LL << 60)
#define kMod        666013
#define edge pair<int, int>
#define x first
#define y second

#define USE_FILES "MLC"

#ifdef USE_FILES
#define cin fin
#define cout fout
ifstream fin("ciur.in");
ofstream fout("ciur.out");
#endif

// number of tests from "in"
int test_cnt = 1;
void clean_test();

// your global variables are here
int n;
bitset<NMAX + 10> sieve;
vector<int> primes;

void do_sieve(int n) {
    primes.push_back(2);
    for (int i = 4; i <= n; i += 2) {
        sieve[i] = 1;
    }

    for (long long i = 3; i <= n; i += 2) {
        if (!sieve[i]) {
            primes.push_back(i);

            for (long long j = 1LL * i * i; j <= n; j += i) {
                sieve[j] = 1;
            }
        }
    }
}

int cb_down(vector<int>& v, const int& x){
  int poz = lower_bound(v.begin(), v.end(), x+1) - v.begin() - 1;

  //  verific daca functia de cautare mi-a gasit elementul dorit
  if(poz >= 0 && poz < (int) v.size() && v[poz] <= x) {
    return poz; // da, elementul exista
  }
  return -1;
}

// your solution is here
void solve() {
    do_sieve(NMAX);

    int n;
    cin >> n;

    int pos = cb_down(primes, n);
    int sol = (pos == -1) ? 0 : pos + 1;
    cout << sol << "\n";

    if (test_cnt > 0) {
        clean_test();
    }
}


void clean_test() {
    // clean if needed
    sieve.reset();
    primes.clear();
}

int main() {
//     cin >> test_cnt;
    while (test_cnt--) {
        solve();
    }

    return 0;
}