#include <bits/stdc++.h>
using namespace std;

#define pb push_back
#define dbg(x) cout << #x << ": " << x << "\n";
#define sz(x) ((int)x.size())

using ll = long long;

const string fn = "ciur";
ifstream fin(fn + ".in");
ofstream fout(fn + ".out");

int n;
bitset<2000005> v;

int main()
{
    fin >> n;
    for (int i = 4; i <= n; i += 2)
        v[i] = 1;
    for (int i = 3; i * i <= n; i += 2)
    {
        if (!v[i])
            for (int j = i * i; j <= n; j += i + i)
                v[j] = 1;
    }
    int ans = 0;
    for (int i = 2; i <= n; ++i)
        ans += !(v[i]);
    fout << ans << '\n';
    return 0;
}