#include <cmath>
#include <vector>
#include <iostream>
using namespace std;

long long harmonic_sum(long long n) {
	long long b = int(sqrt(n));
	long long ans = 0;
	for (int i = 1; i <= b; i++) {
		ans += n / i;
	}
	for (int i = 1; i <= b; i++) {
		long long ql = n / (i + 1) + 1;
		long long qr = n / i + 1;
		long long d = max(qr, b + 1) - max(ql, b + 1);
		ans += d * i;
	}
	return ans;
}

long long harmonic_sum_easy(long long n) {
	long long res = 0;
	for (long long i = 1; i <= n; i++) {
		res += n / i;
	}
	return res;
}

int main() {
	long long n;
	cin >> n;
	long long l = 0, r = 1076832863131 + 10;
	while (r - l > 1) {
		long long m = (l + r) / 2;
		long long res = harmonic_sum(m);
		if (res <= n) {
			l = m;
		} else {
			r = m;
		}
	}
	cout << l << endl;
	return 0;
}