#pragma GCC optimize("O2")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
int main(){
  long long A, B, P, Q;
  cin >> A >> B >> P >> Q;
  B = MOD - B;
  long long x = (A * A + B * 2) % MOD, y = A, N = 2;
  while (true){
    if (N == 998244353) break;
    if (x == P && y == Q){
      cout << N << endl;
      break;
    }
    y = (x * A + y * B) % MOD;
    swap(x, y);
    N++;
  }
}