#include<bits/stdc++.h>

int main() {
	using namespace std;
	cin.tie(nullptr)->sync_with_stdio(false);
	using i64 = int64_t;
	i64 N, L; cin >> N >> L;

	i64 ans = 0;

	auto test = [&](i64 B) -> i64 {
		if (B <= 1) return -1;
		i64 cur = N;
		i64 val = 0;
		vector<i64> digs;

		while (cur) {
			if (cur % B >= 10) return -1;
			digs.push_back(cur % B);
			cur /= B;
		}

		int cnt = int(digs.size());
		bool ok = false;
		if (cnt <= 10) {
			for (int d = cnt-1; d >= 0; --d) {
				val = 10 * val + digs[d];
			}
			if (val >= L) ok = true;
		} else ok = true;
		
		return ok ? B : -1;
	};

	auto check = [&](i64 m, i64 x, i64 y, i64 d) -> bool {
		return (m * m * d + m * x + y < N);
	};

	for (int x = 2; x <= 5e5; ++x) ans = max(ans, test(x));

	for (int x = 1; x <= 9; ++x) {
		for (int y = 0; y <= 9; ++y) {
			i64 K = (N - y)/x;
			ans = max(ans, test(K));
		}
	}

	for (int d = 1; d <= 9; ++d) {
		for (int x = 0; x <= 9; ++x) {
			for (int y = 0; y <= 9; ++y) {

				i64 mi = 0, ma = 1e9;
				while (ma - mi > 1) {
					i64 md = (mi + ma) / 2;
					(check(md, x, y, d) ? mi = md : ma = md);
				}

				ans = max(ans, test(ma));
			}
		}
	}

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