#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define each(e, v) for(auto &e: v)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
//const int MOD = 1000000007;
const int MOD = 998244353;
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
template<typename T> bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;};
template<typename T> bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;};

struct io_setup{
    io_setup(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

struct Random_Number_Generator{
    mt19937_64 mt;

    Random_Number_Generator() : mt(chrono::steady_clock::now().time_since_epoch().count()) {}

    int64_t operator () (int64_t l, int64_t r){ //[l,r)で乱数発生
        uniform_int_distribution<int64_t> dist(l, r-1);
        return dist(mt);
    }

    int64_t operator () (int64_t r){  //[0,r)で乱数発生
        return (*this)(0, r);
    }
};

long long modpow(long long x, long long n, const int &m){
    long long ret = 1;
    for(; n > 0; n >>= 1, x *= x, x %= m){
        if(n&1) ret *= x, ret %= m;
    }
    return ret;
}

template<typename T>
T Euler_Totient(T m){ //オイラーのφ関数(xとmが互いに素ならば、x^φ(m)≡1(mod m))
    T ret = m;
    for(T i = 2; i*i <= m; i++){
        if(m%i == 0) ret /= i, ret *= i-1;
        while(m%i == 0) m /= i;
    }
    if(m > 1) ret /= m, ret *= m-1;
    return ret;
}

int modlog(const int &x, long long y, const int &m){ //x^k=y(mod m)となる最小の非負整数k(xとmは互いに素)
    unordered_map<int, int> mp;
    int n = 0; long long now = 1;
    for(; n*n < m; n++){
        if(!mp.count(now)) mp[now] = n;
        now *= x, now %= m;
    }
    now = modpow(now, Euler_Totient(m)-1, m);
    for(int i = 0; i < n; i++){
        if(mp.count(y)) return n*i+mp[y];
        y *= now, y %= m;
    }
    return -1;
}

template<typename T>
T order(T x, const T &m){ //x^k=1(mod m)となる最小の正整数k(xとmは互いに素)
    T n = Euler_Totient(m);
    vector<T> ds;
    for(T i = 1; i*i <= n; i++){
        if(n%i == 0) ds.push_back(i), ds.push_back(n/i);
    }
    sort(begin(ds), end(ds));
    for(auto &e: ds){
        if(modpow(x, e, m) == 1) return e;
    }
    return -1;
}

template<typename T>
T primitive_root(const T &m){ //素数mの原始根
    vector<T> ds;
    for(T i = 1; i*i <= m-1; i++){
        if((m-1)%i == 0) ds.push_back(i), ds.push_back((m-1)/i);
    }
    sort(begin(ds), end(ds));
    Random_Number_Generator rnd;
    while(true){
        T r = rnd(1, m);
        for(auto &e: ds){
            if(e == m-1) return r;
            if(modpow(r, e, m) == 1) break;
        }
    }
}

vector<ll> mul(vector<ll> a, vector<ll> b){
    vector<ll> c = {a[0]*b[0]+a[1]*b[2], a[0]*b[1]+a[1]*b[3], a[2]*b[0]+a[3]*b[2], a[2]*b[1]+a[3]*b[3]};
    each(e, c) e %= MOD;
    return c;
}

vector<ll> inv(vector<ll> a){
    vector<ll> b = {a[3], MOD-a[1], MOD-a[2], a[0]};
    ll r = ((MOD+a[0])*(MOD+a[3])-a[1]*a[2])%MOD;
    r = modpow(r, MOD-2, MOD);
    each(e, b) e *= r, e %= MOD;
    return b;
}

pll mul(vector<ll> a, pll b){
    pll c = make_pair(a[0]*b.first+a[1]*b.second, a[2]*b.first+a[3]*b.second);
    c.first %= MOD, c.second %= MOD;
    return c;
}

int main(){
    ll X, Y, P, Q; cin >> X >> Y >> P >> Q;

    if(Y == 0){
        if(X == 0){
            assert(P == 0 && Q == 0);
            cout << "2\n";
        }
        else{
            assert(Q*X%MOD == P);
            cout << modlog(X, Q, MOD)+MOD << '\n';
        }
        return 0;
    }

    ll M = 100001;
    vector<ll> A = {X, MOD-Y, 1, 0};
    pll b = make_pair(2, X*modpow(Y, MOD-2, MOD)%MOD);

    map<pll, int> mp;
    vector<ll> B = {1, 0, 0, 1};
    pll c = make_pair(P, Q);

    rep(i, M){
        //if(i == 3) cout << mul(B, b).first << ' ' << mul(B, b).second << '\n';
        mp[mul(B, b)] = i;
        B = mul(B, A);
    }
    B = inv(B);
    vector<ll> C = {1, 0, 0, 1};

    rep(i, M){
        pll p = mul(C, c);
        if(mp.count(p)){
            ll j = M*i+mp[p];
            if(j >= 2){
                cout << j << '\n';
                return 0;
            }
        }
        C = mul(C, B);
    }
}