#include using namespace std; #define rep(i, n) for(int i = 0; i < static_cast(n); ++i) #define per(i, n) for(int i = static_cast(n)-1; i >= 0; --i) #define eee(a) (cerr << (#a) << ": " << (a) << endl); #define ppp(a) (cout << (a) << endl); #define cop(a) for(auto x:(a)){cout << x << endl;} using ll = long long; constexpr int dx[4] = {1, 0, -1, 0}; constexpr int dy[4] = {0, 1, 0, -1}; constexpr char sp = ' '; constexpr ll MOD = 1e9+7; constexpr ll Mod = 998244353; constexpr int INF = 1e9; constexpr ll LINF = 1e18; constexpr double phi = (1+sqrt(5))/2; constexpr double pi = 3.14159265358979323846264338327950288; inline ll gcd(ll a, ll b){return b?gcd(b,a%b):a;} inline ll lcm(ll a, ll b){return a/gcd(a,b)*b;} inline ll inverse(ll n, ll m=MOD){ll a=n,b=m,x=1,y=0;while(b){ll t=a/b;a-=t*b;swap(a,b);x-=t*y;swap(x,y);}return (a%m+m)%m;} inline void Yes(){puts("Yes");} inline void No(){puts("No");} inline void Judge(bool b){b?Yes():No();} inline void YES(){puts("YES");} inline void NO(){puts("NO");} inline void JUDGE(bool b){b?YES():NO();} inline ll powmod(ll b, ll e, ll m=MOD){ll r=1;while(e>0){if(e&1)r=(r%m)*(b%m)%m;b=(b%m)*(b%m)%m;e>>=1;}return r;} inline double distance(ll x1, ll y1, ll x2, ll y2){return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));} inline double d2r(double d){return d*pi/180;} inline double r2d(double r){return r*180/pi;} templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b ostream& operator<<(ostream& s, const pair& p) {return s << "(" << p.first << ", " << p.second << ")";} template ostream& operator<<(ostream& s, const vector& v) { s<<'[';for(size_t i=0;i> n >> m; if(n <= m){ cout << 1 << '\n'; return 0; } if(n%2 or n%2 == 0 and n > 2*m){ cout << -1 << '\n'; return 0; } cout << 2 << '\n'; return 0; }