#include using namespace std; #include namespace mp = boost::multiprecision; #include using namespace atcoder; template inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false)); } template inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false)); } #define rep(i, n) for (long long i = 0; i < (long long)(n); i++) #define rep2(i, m ,n) for (int i = (m); i < (long long)(n); i++) #define REP(i, n) for (long long i = 1; i < (long long)(n); i++) typedef long long ll; #define updiv(N,X) (N + X - 1) / X #define l(n) n.begin(),n.end() #define YesNo(Q) Q==1?cout<<"Yes":cout<<"No" using P = pair; using mint = modint; const int MOD = 998244353LL; const ll INF = 999999999999LL; vector fact, fact_inv, inv; /* init_nCk :二項係数のための前処理 計算量:O(n) */ template void input(vector &v){ rep(i,v.size()){cin>>v[i];} return; } void init_nCk(int SIZE) { fact.resize(SIZE + 5); fact_inv.resize(SIZE + 5); inv.resize(SIZE + 5); fact[0] = fact[1] = 1; fact_inv[0] = fact_inv[1] = 1; inv[1] = 1; for (int i = 2; i < SIZE + 5; i++) { fact[i] = fact[i - 1] * i % MOD; inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD; fact_inv[i] = fact_inv[i - 1] * inv[i] % MOD; } } /* nCk :MODでの二項係数を求める(前処理 int_nCk が必要) 計算量:O(1) */ long long nCk(int n, int k) { assert(!(n < k)); assert(!(n < 0 || k < 0)); return fact[n] * (fact_inv[k] * fact_inv[n - k] % MOD) % MOD; } long long modpow(long long a, long long n, long long mod) { long long res = 1; while (n > 0) { if (n & 1) res = res * a % mod; a = a * a % mod; n >>= 1; } return res; } ll POW(ll a,ll n){ long long res = 1; while (n > 0) { if (n & 1) res = res * a; a = a * a; n >>= 1; } return res; } template T tfloorsum(T n, T a, T b, T m) { if (n == 0) return 0; T res = 0; if (a >= m) { res += n * (n - 1) * (a / m) / 2; a %= m; } if (b >= m) { res += n * (b / m); b %= m; } if (a == 0) return res; T ymax = (a * n + b) / m, xmax = ymax * m - b; if (ymax == 0) return res; res += (n - (xmax + a - 1) / a) * ymax; res += tfloorsum(ymax, m, (a - xmax % a) % a, a); return res; } int main(){ mp::int128_t a,b,c,d;cin>>a>>b>>c>>d; if(a*d>c*b){swap(a,c);swap(b,d);} if(a*d==c*b){cout << -1 << endl;return 0;} mp::int128_t ft = updiv(b*d,(c*b-a*d)); //cout << ft << endl; cout << ft-1-(tfloorsum(ft,2*c,d,2*d)-tfloorsum(ft,2*a,b,2*b)) << endl; }