#define LOCAL
#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>
using namespace std;

#define rep(i,s,n) for (int i = (ll)s; i < (ll)n; i++)
#define rrep(i,n,e) for (int i = (ll)n; i > (ll)e; i--)
#define ll long long
#define ld long double
#define pb push_back
#define eb emplace_back
#define All(x) x.begin(), x.end()
#define Range(x, i, j) x.begin() + i, x.begin() + j
// #define M_PI 3.14159265358979323846 // CF
#define deg2rad(deg) ((((double)deg)/((double)360)*2*M_PI))
#define rad2deg(rad) ((((double)rad)/(double)2/M_PI)*(double)360)
#define Find(set, element) set.find(element) != set.end()
#define Decimal(x) cout << fixed << setprecision(10) << x << endl; // print Decimal number 10 Rank
#define endl "\n"
#define Case(x) printf("Case #%d: ", x); // gcj

typedef pair<int, int> PI;
typedef pair<ll, ll> PLL;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<vector<int>>> vvvi;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<vector<vector<ll>>> vvvl;
typedef vector<PI> vpi;
typedef vector<vector<PI>> vvpi;
typedef vector<PLL> vpl;
typedef vector<vector<PLL>> vvpl;
typedef vector<char> vch;
typedef vector<vector<char>> vvch;

constexpr ll LINF = 8001002003004005006ll;
constexpr int INF = 1002003004;
constexpr int n_max = 2e5+10;

template<class T>
inline bool chmax(T &a, T b) { if(a<b) { a=b; return true; } return false; };
template<class T>
inline bool chmin(T &a, T b) { if(a>b) { a=b; return true; } return false; };

template<class T, class U>
T POW(T x, U n) {T ret=1; while (n>0) {if (n&1) {ret*=x;} x*=x; n>>=1;} return ret;};

// debug
template <typename A, typename B>
string to_string(pair<A, B> p);
string to_string(const string &s) {return '"' + s + '"';};
string to_string(const char c) {return to_string((string) &c);};
string to_string(bool b) {return (b ? "true" : "false");};
template <size_t N>
string to_string(bitset<N> v){
  string res = "";
  for(size_t i = 0; i < N; i++) res += static_cast<char>('0' + v[i]);
  return res;
};
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for(const auto &x : v) {
    if(!first) res += ", ";
    first = false; res += to_string(x);
  }
  res += "}";
  return res;
};
template <typename A, typename B>
string to_string(pair<A, B> p){return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";}

void debug_out() {cerr << endl;};
template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T) { cerr << " " << to_string(H); debug_out(T...); };

void LINE_OUT() {
  cout << "--------------" << endl;
};

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define LINE LINE_OUT();
#else
#define debug(...) 71
#define LINE 71;
#endif

void print() { cout << endl; }
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
  cout << head;
  if (sizeof...(tail) != 0) cout << " ";
  print(forward<Tail>(tail)...);
};

template <class T>
void print(vector<T> &vec) {
  for (auto& a : vec) {
    cout << a;
    if (&a != &vec.back()) cout << " ";
  }
  cout << endl;
};

template <class T>
void print(vector<vector<T>> &df) {
  for (auto& vec : df) {
    print(vec);
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  ll X, Y, A, B; cin >> X >> Y >> A >> B;
  ll x = X; // 強さ
  ll ans = 0;

  while (1) {
    if ((ld)x * (ld)A > INF) {
      ll diff = Y - x -1;
      if (diff <= 0) break;
      ans += (diff/B);
      break;
    } else if (x * A > Y-1) {
      ll diff = Y - x -1;
      if (diff <= 0) break;
      ans += (diff/B);
      break;
    } else {
      if (x * A <= x + B) {
        x = x * A;
        ans++;
      } else {
        ll diff = x * A - x;
        ans += (diff/B);
        x = x + (diff/B) * B;
      }
    }
  }

  cout << ans << endl;


  return 0;
};

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <vector>
#include <ctime>
#include <cctype>
#include <bitset>
#include <utility>
#include <complex>
#include <iomanip>
#include <numeric>
#include<unordered_set>
#include <climits>//INT_100010n
#include <regex>
#include<deque>
//#include<bits/stdc++.h>
#define PP pair<ll,int>
#define inf 0x3f3f3f3f
#define INF 0x7fffffff
#define llinf 0x3f3f3f3f3f3f3f3fll
#define dinf 1000000000000.0
#define PI 3.1415926
#define LL unsigned int
#define wc 1e-18
typedef long long ll;
using namespace std;
const ll mod=1e9+7;
ll x,y,a,b,ct;
int main()
{
    cin>>x>>y>>a>>b;
    while(x<y/a&&x<(x+b)/a){
        ct++;
        x=x*a;
    }
    ct=ct+(y-1-x)/b;
    cout<<ct<<endl;
    return 0;
}


