#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 998244353;
constexpr bool debug = false;
//---------------------------------//

namespace tk {
template<typename T>
T ext_gcd(const T & a, T & x, const T & b, T & y) {
	assert(a > 0);
	assert(b > 0);
	T a0 = a, a1 = 1, a2 = 0, b0 = b, b1 = 0, b2 = 1;
	while (b0 > 0) {
		T q = a0 / b0, r = a0 % b0;
		T nb1 = a1 - q * b1, nb2 = a2 - q * b2;
		a0 = b0; b0 = r;
		a1 = b1; b1 = nb1;
		a2 = b2; b2 = nb2;
	}
	x = a1;
	y = a2;
	return a0;
}
} // namespace tk


int main() {
	int A, B;
	cin >> A >> B;
	int x, y;
	int g = tk::ext_gcd(A, x, B, y);
	if (g != 1) puts("-1");
	else {
		if (x >= 0) { swap(A, B); swap(x, y); }
		int ans = 0;
		const int ab = A * B;
		int basel = -A * x, baser = B * y;
		int l = basel, r = baser;
		for (int k = 1; r - l < ab; ++k, l += basel, r += baser) {
			int d = r / ab * ab;
			if (d < l) ++ans;
		}
		cout << ans << endl;
	}
}