#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={0,1,-1,0,1,1,-1,-1,0};
const ll dx[9]={1,0,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

const int mod = MOD9;
const int max_n = 200005;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }
  bool operator==(const mint &p) const { return x == p.x; }
  bool operator!=(const mint &p) const { return x != p.x; }
  bool operator<(const mint &p) const { return x < p.x; }
  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}
using vm=vector<mint>;
using vvm=vector<vm>;

vvm matmul(vvm left,vvm right){
    ll m=left.size();
    vvm ret(m,vm(m,0));
    rep(i,m)rep(j,m)rep(k,m){
      ret[i][j]+=left[i][k]*right[k][j];
    }
    return ret;
}

int main(){
  mint a,b,p,q;cin >> a >> b >> p >> q;
  if(b==0){
    ll m=100010;
    map<mint,ll> mp;
    mint now=1;
    rep(i,m){
      mp[now]=i;
      now*=a;
    }
    mint to=p;
    rep(i,m){
      if(mp.count(to)){
        if(i*m+mp[to])
        cout << i*m+mp[to] <<endl;return 0;
      }
      to/=now;
    }
  }
  else{
    ll m=100010;
    map<vm,ll> mp;
    vvm now(2,vm(2));now[0][0]=1,now[1][1]=1;
    vvm A(2,vm(2));A[0][0]=a,A[0][1]=-b,A[1][0]=1;
    rep(i,m){
      vm x(2);
      x[0]=now[0][0]*2+now[0][1]*a/b;
      x[1]=now[1][0]*2+now[1][1]*a/b;
      mp[x]=i;
      now=matmul(A,now);
    }
    vvm iA=A;swap(iA[0][0],iA[1][1]);iA[1][0]*=-1,iA[0][1]*=-1;
    mint det=A[0][0]*A[1][1]-A[0][1]*A[1][0];
    rep(i,2)rep(j,2)iA[i][j]/=det;
    vm to={p,q};
    rep(i,m){
      if(mp.count(to)){
        cout << i*m+mp[to] <<endl;return 0;
      }
      vm nto(2);
      nto[0]=iA[0][0]*to[0]+iA[0][1]*to[1];
      nto[1]=iA[1][0]*to[0]+iA[1][1]*to[1];
      to=nto;
    }
  }
}