#include <bits/stdc++.h>
using namespace std;

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__); // __VA_ARGS__可変引数マクロ
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
template<typename T>void MACRO_OUT(const T t) { std::cout << t; }
template<typename First, typename...Rest>void MACRO_OUT(const First first, const Rest...rest) { std::cout << first << " "; MACRO_OUT(rest...); }
#define OUT(...) MACRO_OUT(__VA_ARGS__);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist); // std::fixed 浮動小数点の書式 / setprecision 浮動小数点数を出力する精度を設定する。
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T & a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;
 
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double eps = 1e-7;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T & val) { for (auto& x : a) x = val; }   //  int a[5] = {1,2,3,4,5};	FILL(a,10);
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T & val) { for (auto& b : a) FILL(b, val); }  // ２次元配列でもそのまま使える
template<class T> void FILL(std::vector<T> & a, const T & val) { for (auto& x : a) x = val; }   //	使い方 vector<int> a(3);	FILL(a,10);
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>> & a, const T & val) { for (auto& b : a) FILL(b, val); }  // ２次元配列でもそのまま使える
// ------------>8------------------------------------->8------------


int main() {
INIT;

// VAR(ld,x,y,a,b)
VAR(ll,x,y,a,b)
// ld n = log(b /x) / log(a);  // これだと、小数点桁落ちで、正確に値がでない

ll ans =0;
// for (int i = 1; x < b; i++) {
while(1){
    if( x >= y /a ) break;  
    // if(a*x >= y) break;
    if(a*x >= x+b) break;
    x *= a;
    ans++;
}

// ll ans = (y - pow(a,n) * x ) / b;
ans += (y - 1 - x ) / b;

OUT(ans)

return 0;
}

#include<iostream>
#include<vector>
#include<cmath>
using namespace std;

int main(){
    long long X, Y, A, B;
    std::cin >> X >> Y >> A >> B;

    long long exp = 0;
    int flg_A = 0, flg_B = 0;

    while(flg_A == 0){
        if(X*(A - 1) < B && (double)X*A < 2e18){
            if(X*A < Y){
                X = X*A;
                exp++;
            }else{
                flg_A = 1;
                flg_B = 1;
            }
        }else{
            flg_A = 1;
        }
    }
    // std::cout << exp;    
    // std::cout << (long long)round(floorl(((double)Y - (double)X - 1.0)/(double)B));

    //あとはずっとB
    if(flg_B == 0){
        exp = exp + (Y - X - 1)/B;
    }

    std::cout << exp;    

}