#include <bits/stdc++.h>

using namespace std;

#if 1
    #define pv(x) cout<<#x<<" = "<<(x)<<"; ";cout.flush()
    #define pn cout<<endl
#else
    #define pv(x)
    #define pn
#endif

#ifdef INFOARENA
    ifstream in("ciur.in");
    ofstream out("ciur.out");
#else
    #define in cin
    #define out cout
#endif

using ll = long long;
using ull = unsigned long long;
using uint = unsigned int;
using ld = long double;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pld = pair<ld, ld>;
#define pb push_back
const double PI = 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862;
const int inf_int = 1e9 + 5;
const ll inf_ll = 1e18 + 5;
const int NMax = 1e3 + 5;
const int dx[] = {-1,0,0,+1}, dy[] = {0,-1,+1,0};

int main() {
    cin.sync_with_stdio(false);
    cin.tie(0);

    int N, count = 0;
    in >> N;
    vector<int> prime, lp(N+1);
    for (int i = 2; i <= N; ++i) {
        if (lp[i] == 0) {
            prime.pb(i);
            lp[i] = i;
            ++count;
        }

        for (int j = 0; prime[j] <= lp[i] && i * prime[j] <= N; ++j) {
            lp[i * prime[j]] = prime[j];
        }
    }
    
    // for (int p : prime) {
    //     out << p << ' ';
    // }

    out << count << '\n';

    return 0;
}