#include <bits/stdc++.h>

using namespace std;

int main() {
	#ifdef BLAT
		freopen("input", "r", stdin);
	#else
		freopen("ciur.in", "r", stdin);
		freopen("ciur.out", "w", stdout);
	#endif

	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);

	int n;
	cin >> n;

	vector< bool > prim(n + 1);
	int ans = 1;
	for(int i = 3; i <= n; i += 2) {
		if(!prim[i]) {
			++ans;
			for(long long j = 1ll*i*i; j <= n; j += 2*i) {
				prim[j] = true;
			}
		}
	}

	cout << ans << '\n';
	return 0;
}