#include <iostream> #include <iomanip> #include <cstdio> #include <string> #include <cstring> #include <deque> #include <list> #include <queue> #include <stack> #include <vector> #include <utility> #include <algorithm> #include <map> #include <set> #include <complex> #include <cmath> #include <limits> #include <cfloat> #include <climits> #include <ctime> #include <cassert> #include <numeric> #include <functional> using namespace std; #define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++) #define repq(i,a,n) for(int (i)=(a); (i)<=(n); (i)++) #define repr(i,a,n) for(int (i)=(a); (i)>=(n); (i)--) #define int long long int template<typename T> void chmax(T &a, T b) {a = max(a, b);} template<typename T> void chmin(T &a, T b) {a = min(a, b);} template<typename T> void chadd(T &a, T b) {a = a + b;} typedef pair<int, int> pii; typedef long long ll; int dx[] = {0, 0, 1, -1}; int dy[] = {1, -1, 0, 0}; constexpr ll INF = 1001001001001001LL; constexpr ll MOD = 1000000007LL; signed main() { int N, M; cin >> N >> M; if(N % 2 == 1) cout << (M >= N ? 1 : -1) << endl; else { if(M < N / 2) cout << -1 << endl; else if(M >= N) cout << 1 << endl; else cout << 2 << endl; } return 0; }