#include using namespace std; // 基本テンプレート struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star; #define P(x) cout << (x) << endl #define p(x) cout << (x) #define all(c) (c).begin(), (c).end() #define rall(c) (c).rbegin(), (c).rend() #define mat(type, c, m, n) vector> c(m, vector(n));for(auto& r:c)for(auto& i:r)cin>>i; #define rep(i,a,n) for(int i=(a), i##_len=(n); in; --i) #define each(x,y) for(auto &(x):(y)) #define perm(c) sort(all(c));for(bool c##p=1;c##p;c##p=next_permutation(all(c))) #define cauto const auto& #define UNIQUE(v) v.erase( unique(all(v)), v.end() ); #define len(x) ((int)(x).size()) #define length(a) (sizeof(a)/sizeof(a[0])) inline void print() {cout << endl;} template inline void print(H h, T... t){cout << h << " ";print(t...);} #define dbg(v) for(auto i : v) cout << i << " "; cout << endl; // 型 typedef long long ll; typedef vector vi; typedef vector vd; typedef vector vll; typedef vector vs; // 4近傍 //int dy[]={0, 1, 0, -1}; //int dx[]={1, 0, -1, 0}; // 8近傍 //constexpr int dy[]={0,0,1,-1,1,1,-1,-1}; //constexpr int dx[]={1,-1,0,0,1,-1,1,-1}; ll mod = (int)1e9 + 7; // 定数 #define PI acos(-1.0) constexpr int EPS = (1e-9); constexpr int INF = 100000000; vector v(400000000, true); int f() { ll n, d; cin >> n >> d; if (n == d) { return 0; } else if (d == 1 || n == d + 1) { return n - 1; } else if (n % d == 0) { return n / d - 1; } ll ans = -1; v[0] = false; ll a = 0; rep(i, 0, n) { // print(i, a); if (v[(a + d) % n]) { v[a + d] = false; a = (a + d) % n; ++ans; } else { break; } } return ans; } int main() { // cout << setprecision(12) << fixed; P(f()); return 0; }