#include <bits/stdc++.h>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n, nr = 1, a[2000001];

int main()
{
    f >> n;

    for (long long i = 3; i <= n; i += 2) {
        if (!a[i]) {
            nr++;

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

    g << nr;

    g.close();

    return 0;
}