#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i,n)for (int i = 0; i < int(n); ++i)
#define rrep(i,n)for (int i = int(n)-1; i >= 0; --i)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template<class T> void chmax(T& a, const T& b) {a = max(a, b);}
template<class T> void chmin(T& a, const T& b) {a = min(a, b);}
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

template<class T, int N>
struct Mat: std::array<std::array<T, N>, N> {
    friend Mat<T, N> operator*(const Mat& A, const Mat& B) {
        Mat<T, N> C = {};
        for(int i = 0; i < N; i++) {
            for(int k = 0; k < N; k++) {
                for(int j = 0; j < N; j++) {
                    C[i][j] += A[i][k] * B[k][j];
                }
            }
        }
        return C;
    }
    friend std::array<T, N> operator*(const Mat& A, const std::array<T, N>& v) {
        std::array<T, N> x = {};
        for(int i = 0; i < N; i++) for(int j = 0; j < N; j++) x[i] += A[i][j] * v[j];
        return x;
    }
    friend Mat<T, N> operator+(const Mat& A, const Mat& B) {
        Mat<T, N> C;
        for(int i = 0; i < N; i++) {
            for(int j = 0; j < N; j++) {
                C[i][j] = A[i][j] + B[i][j];
            }
        }
        return C;
    }
    Mat<T, N>& operator*=(const Mat& A) { return *this = *this * A; }
    Mat<T, N>& operator+=(const Mat& A) {
        for(int i = 0; i < N; i++) {
            for(int j = 0; j < N; j++) {
                (*this)[i][j] += A[i][j];
            }
        }
    }
    static Mat<T, N> I() {
        Mat<T, N> X = {};
        for(int i = 0; i < N; i++) X[i][i] = 1;
        return X;
    }
    Mat<T, N> pow(long long k) const {
        assert(k >= 0);
        auto X = *this;
        auto Y = I();
        while(k) {
            if (k & 1) Y *= X;
            k >>= 1;
            if (k) X *= X;
        }
        return Y;
    }
    Mat<T, N> inv() const {
        auto X = *this;
        auto Y = I();
        for(int p = 0; p < N; p++) {
            bool ok = false;
            for(int i = p; i < N; i++) {
                if (X[i][p] != T()) {
                    ok = true;
                    if (i != p) {
                        // std::swap(X[i], X[p]);
                        for(int j = p; j < N; j++) std::swap(X[i][j], X[p][j]);
                        std::swap(Y[i], Y[p]);
                    }
                    break;
                }
            }
            assert(ok);
            T c = 1 / X[p][p];
            for(int j = p; j < N; j++) X[p][j] *= c;
            for(int j = 0; j < N; j++) Y[p][j] *= c;
            for(int i = 0; i < N; i++) if (i != p) {
                T c = X[i][p];
                for(int j = p; j < N; j++) X[i][j] -= c * X[p][j];
                for(int j = 0; j < N; j++) Y[i][j] -= c * Y[p][j];
            }
        }
        return Y;
    }

    T det() const {
        if (N == 0) return T();
        auto X = *this;
        bool flag = false;
        T res = 1;
        bool ok = false;
        for(int p = 0; p < N; p++) {
            for(int i = p; i < N; i++) {
                if (X[i][p] != T()) {
                    ok = true;
                    if (i != p) {
                        flag = !flag;
                        for(int j = p; j < N; j++) std::swap(X[i][j], X[p][j]);
                    }
                    break;
                }
            }
            if (!ok) return T();
            // T = modint
            for(int i = p + 1; i < N; i++) {
                T c0 = 1, c1 = 0, d0 = 0, d1 = 1;
                int a = X[p][p].val(), b = X[i][p].val();
                while(true) {
                    if (b == 0) {
                        break;
                    }
                    int q = a / b;
                    a -= q * b;
                    c0 -= q * d0;
                    c1 -= q * d1;
                    if (a == 0) {
                        flag = !flag;
                        for(int j = p; j < N; j++) std::swap(X[i][j], X[p][j]);
                        std::swap(c0, d1);
                        std::swap(c1, d0);
                        break;
                    }
                    q = b / a;
                    b -= q * a;
                    d0 -= q * c0;
                    d1 -= q * c1;
                }
                for(int j = p; j < N; j++) {
                    T a = X[p][j], b = X[i][j];
                    T x = c0 * a + c1 * b, y = d0 * a + d1 * b;
                    X[p][j] = x;
                    X[i][j] = y;
                }
            }
            res *= X[p][p];
        }
        if (flag) res = -res;
        return res;
    }
    friend std::ostream& operator<<(std::ostream& os, const Mat<T, N>& A) {
        for(int i = 0; i < N; i++) for(int j = 0; j < N; j++) os << A[i][j] << " \n"[j + 1 == N];
        return os;
    }
};

std::ostream& operator<<(std::ostream& os, const mint& x) {
    return os << x.val();
}

template<class mint>
int BSGS(mint a, mint b) {
    // constraint: a.inv() is defined if a != 0
    // returns x s.t. a ^ x = b
    const int p = mint::mod();
    if (p == 1) return 0;
    if (a == 0) {
        if (b == 0) return 1;
        else if (b == 1) return 0;
        else return -1;
    }
    const int sq_ceil = [p]{
        int l = 0, r = 46340;
        while(r - l > 1) {
            int c = (r + l) >> 1;
            (c * c >= p ? r : l) = c;
        }
        return r;
    }();
    std::unordered_map<int, int> log_a;

    mint aj = 1;
    for(int j = 0; j < sq_ceil; j++, aj *= a) {
        if (!log_a.count(aj.val())) {
            log_a[aj.val()] = j;
        }
    }

    mint a_inv = a.inv();
    mint step = a_inv.pow(sq_ceil);
    mint t = b;
    for(int i = 0; i < p; i += sq_ceil, t *= step) {
        auto it = log_a.find(t.val());
        if (it != log_a.end()) return i + it->second;
    }
    return -1;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int a, b, p, q;
    cin >> a >> b >> p >> q;
    if (b == 0) {
        if (a == 0) {
            cout << 2 << '\n';
        } else {
            // a^(n-1) = q
            int n = BSGS<mint>(a, mint(q) / a) + 2;
            cout << n << '\n';
        }
        return 0;
    }
    Mat<mint, 2> X{array<mint, 2>{a, -b}, array<mint, 2>{1, 0}};
    array<mint, 2> v{a, 2};
    v = X * v;
    unordered_map<ll, int> log_a;
    for(int j = 0; j < 100000; j++) {
        ll t = v[0].val() | ll(v[1].val()) << 32;
        if (!log_a.count(t)) log_a[t] = j;
        v = X * v;
    }
    auto Y = X.inv().pow(100000);
    v = array<mint, 2>{p, q};
    for(int i = 0; i < 100000; i++) {
        ll t = v[0].val() | ll(v[1].val()) << 32;
        auto it = log_a.find(t);
        if (it != log_a.end()) {
            cout << 100000LL * i + it->second + 2 << '\n';
            break;
        }
        v = Y * v;
    }
}