#include<iostream>
#include<algorithm>
#include<vector>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
#include<array>
template<typename T,unsigned int N>
struct Matrix{
	array<array<T,N>,N>dat;
	array<T,N>&operator[](int i){return dat[i];}
	const array<T,N>&operator[](int i)const{return dat[i];}
	static Matrix eye(){
		Matrix res;
		for(int i=0;i<N;i++)res[i][i]=1;
		return res;
	}
	Matrix operator+(const Matrix&A)const{
		Matrix res;
		for(int i=0;i<N;i++)for(int j=0;j<N;j++)
			res[i][j]=dat[i][j]+A[i][j];
		return res;
	}
	Matrix operator*(const Matrix&A)const{
		Matrix res;
		for(int i=0;i<N;i++)for(int k=0;k<N;k++)for(int j=0;j<N;j++)
			res[i][j]+=dat[i][k]*A[k][j];
		return res;
	}
	Matrix pow(long long n)const{
		Matrix a=*this,res=eye();
		for(;n;a=a*a,n>>=1)if(n&1)res=res*a;
		return res;
	}
};
using mat=Matrix<mint,2>;
int A,B,P,Q;
main()
{
	cin>>A>>B>>P>>Q;
	int sqP=2e5;
	mat X;
	X[0][0]=A;X[0][1]=-B;X[1][0]=1;X[1][1]=0;
	mat E=X.pow(sqP);
	vector<pair<pair<int,int>,int> >tb(sqP);
	pair<int,int>e=make_pair(P,Q);
	for(int i=0;i<sqP;i++)
	{
		e=make_pair((X[0][0]*e.first+X[0][1]*e.second).val(),(X[1][0]*e.first+X[1][1]*e.second).val());
		tb[i]=make_pair(e,-i-1);
	}
	sort(tb.begin(),tb.end());
	e=make_pair(((mint)A*A-2*B).val(),A);
	for(long s=0;;)
	{
		e=make_pair((E[0][0]*e.first+E[0][1]*e.second).val(),(E[1][0]*e.first+E[1][1]*e.second).val());
		s+=sqP;
		auto it=lower_bound(tb.begin(),tb.end(),make_pair(e,-sqP));
		if(it!=tb.end()&&it->first==e)
		{
			long N=s+it->second+2;
			cout<<N<<endl;
			return 0;
		}
	}
}