#include <stdio.h>

#define DIM 2
const int Mod = 998244353;

void copy_matrix(int d, long long A[][DIM], long long B[][DIM])
{
	int i, j;
	for (i = 0; i < d; i++) for (j = 0; j < d; j++) B[i][j] = A[i][j];
}

void prod_matrix(int d, long long A[][DIM], long long B[][DIM], long long C[][DIM])
{
	int i, j, k;
	for (i = 0; i < d; i++) {
		for (j = 0; j < d; j++) {
			for (k = 0, C[i][j] = 0; k < d; k++) C[i][j] += A[i][k] * B[k][j] % Mod;
			C[i][j] %= Mod;
		}
	}
}

void pow_matrix(int d, long long A[][DIM], long long k, long long B[][DIM])
{
	int i, j;
	long long C[2][DIM][DIM], D[DIM][DIM];
	copy_matrix(d, A, C[0]);
	for (i = 0; i < d; i++) for (j = 0; j < d; j++) B[i][j] = 0;
	for (i = 0; i < d; i++) B[i][i] = 1;
	for (i = 0, j = 1; k > 0; i ^= 1, j ^= 1, k >>= 1) {
		prod_matrix(d, C[i], C[i], C[j]);
		if (k % 2 == 1) {
			prod_matrix(d, B, C[i], D);
			copy_matrix(d, D, B);
		}
	}
}

void copy_vector(int d, long long x[], long long y[])
{
	int i;
	for (i = 0; i < d; i++) y[i] = x[i];
}

void prod_matrix_vector(int d, long long A[][DIM], long long x[], long long y[])
{
	int i, j;
	for (i = 0; i < d; i++) {
		for (j = 0, y[i] = 0; j < d; j++) y[i] += A[i][j] * x[j] % Mod;
		y[i] %= Mod;
	}
}

#define HASH 200003
const int H_Mod = HASH;

typedef struct List {
	struct List *next;
	int N;
	long long z[DIM];
} list;

int hash_func(long long x[])
{
	return ((x[0] << 20) + x[1]) % H_Mod;
}

int main()
{
	long long A, B, P, Q;
	scanf("%lld %lld %lld %lld", &A, &B, &P, &Q);
	
	int h, i;
	long long S[DIM][DIM] = {{0, 1}, {Mod - B, A}}, T[DIM][DIM], x[DIM] = {2, A}, z[DIM];
	list *hash[HASH] = {}, d[100001], *p;
	for (i = 1; i <= 100000; i++) {
		pow_matrix(2, S, (long long)i * 100000, T);
		prod_matrix_vector(2, T, x, z);
		d[i].N = i;
		d[i].z[0] = z[0];
		d[i].z[1] = z[1];
		h = hash_func(z);
		for (p = hash[h]; p != NULL; p = p->next) if (p->z[0] == z[0] && p->z[1] == z[1]) break;
		if (p == NULL) {
			d[i].next = hash[h];
			hash[h] = &(d[i]);
		}
	}
	for (i = 0, z[0] = Q, z[1] = P; i < 100000; i++) {
		h = hash_func(z);
		for (p = hash[h]; p != NULL; p = p->next) if (p->z[0] == z[0] && p->z[1] == z[1] && (long long)p->N * 100000 - i + 1 >= 2) break;
		if (p != NULL) break;
		copy_vector(2, z, x);
		prod_matrix_vector(2, S, x, z);
	}
	printf("%lld\n", (long long)p->N * 100000 - i + 1);
	fflush(stdout);
	return 0;
}