//Author: hyperion_1724
//Time and Date: 16:55:26  17 October 2020

//Optional FAST
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,fma,abm,mmx,avx,avx2,tune=native")

//Required Libraries

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>

//Required namespaces

using namespace std;
using namespace __gnu_pbds;

//Required defines

#define endl '\n'

#define READ(X) cin>>X;
#define READV(X) long long X; cin>>X;
#define READAR(A,N) long long A[N]; for(long long i=0;i<N;i++) {cin>>A[i];}
#define rz(A,N) A.resize(N);
#define sz(X) (long long)(X.size())
#define pb push_back
#define pf push_front
#define fi first
#define se second
#define FORI(a,b,c) for(long long a=b;a<c;a++)
#define FORD(a,b,c) for(long long a=b;a>c;a--)

//Required typedefs

template <typename T> using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
template <typename T> using ordered_set1 = tree<T,null_type,greater<T>,rb_tree_tag,tree_order_statistics_node_update>;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;

//Required Constants

const long long inf=(long long)1e18;
const long long MOD=(long long)(1e9+7);
const long long INIT=(long long)(1e6+1);
const long double PI=3.14159265358979;

// Required random number generators

// mt19937 gen_rand_int(chrono::steady_clock::now().time_since_epoch().count());
// mt19937_64 gen_rand_ll(chrono::steady_clock::now().time_since_epoch().count());

//Required Functions

ll power(ll x,ll y) 
{ 
    if (y == 0) 
        return 1; 
    ll p = power(x, y/2) % MOD; 
    p = (p * p) % MOD; 
  
    return (y%2 == 0)? p : (x * p) % MOD; 
}
ll modInverse(ll a) 
{ 
   return power(a,MOD-2); 
   
}

//Work

int main()
{
    #ifndef ONLINE_JUDGE
    if (fopen("INPUT.txt", "r"))
    {
        freopen ("INPUT.txt" , "r" , stdin);
        //freopen ("OUTPUT.txt" , "w" , stdout);
    }
    #endif
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    clock_t clk;
    clk = clock();
//-----------------------------------------------------------------------------------------------------------//

    READV(X);
    READV(Y);
    READV(A);
    READV(B);
    ll exp=0;
    ll curr=0;
    while (X<Y)
    {
        exp=max(exp,curr+((Y-X-1)/B));
        if(((Y-1)/X)>=A)
        {
            curr++;
            X=X*A;
        }
        else
        {
            break;
        }
    }
    cout<<exp<<endl;
    

//-----------------------------------------------------------------------------------------------------------//


    clk = clock() - clk;
    cerr << fixed << setprecision(6) << "Time: " << ((double)clk)/CLOCKS_PER_SEC << endl;

    return 0;
}
#ifdef Prateek
  #include "\Prateek.h"
#else
  #include <bits/stdc++.h>
  using namespace std;
  #define debug(...) 42
#endif
#define F first
#define S second
#define pb push_back
#define f(i,x,n) for(int i=x;i<n;i++)
#define all(c) c.begin(),c.end()
#define int ll
using ll = long long;
const int MOD = 1e9+7, N = 1e5 + 10; 

using i128 = __int128_t;

int32_t main(){
   ios::sync_with_stdio(false);
   cin.tie(NULL);
   int x, y, a, b;
   cin >> x >> y >> a >> b;
   int cnt = 0;
   i128 n = x;
   i128 m = y;
   while(n < m) {
      i128 na = n*a;
      i128 nb = n+b;
      if(na <= nb) {
         ++cnt;
         n = na;
      } else {
         i128 r = na;
         if(na > y) {
            r = y;
         }
         r = (r-n+b-1) / b;
         n += r*b;
         cnt += r;
      }
   }
   cout << cnt-1 << '\n';
   return 0;
}