#include <bits/stdc++.h>

using namespace std;
 
#define int unsigned long long
 
#define PB    push_back
#define ALL(x)    (x).begin(), (x).end()
#define ALLR(x)    (x).rbegin(), (x).rend()
#define MP    make_pair

template <typename A, typename B>
string to_string(pair<A, B> p);
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
 
string to_string(const string& s) {
  return '"' + s + '"';
}
 
string to_string(const char* s) {
  return to_string((string) s);
}
 
string to_string(bool b) {
  return (b ? "true" : "false");
}
 
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
 
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) + ")";
}
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
 
void debug_out() { cerr << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef KILLBUG
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

#define FAST_IO ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)

typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;
typedef vector<string> vs;
typedef vector<bool> vb;
 
const int INF = LONG_LONG_MAX/10;
const double PI = 3.141592653589793238;
const int MOD = 998244353;

bool many = false;
struct Solve {
    string endl = "\n";
    
    Solve() {
		int x, y, a, b;
		cin >> x >> y >> a >> b;
		
		int str = x;
		int exp = 0;

		for (int i = 0; str < b/(a-1) && str*a < y; i++) {
			str *= a;
			exp++;
		}
		debug(str, exp);
		if (str < y) {
			exp += (y-str-1)/b;
		}
		
		cout << exp << endl;
	}
};

signed main() {
    FAST_IO;
    int CASES=1;
    if (many)
        cin >> CASES;
    for (int i = 1; i <= CASES; i++) {
        Solve me;
    }
}
// g++ -Wall -Wextra -pedantic -std=c++17 -O2 -Wshadow -Wformat=2 -Wfloat-equal -Wconversion -Wlogical-op -Wshift-overflow=2 -Wduplicated-cond -Wcast-qual -Wcast-align -D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -D_FORTIFY_SOURCE=2 -fsanitize=address -fsanitize=undefined -fno-sanitize-recover -fstack-protector

#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define db double
#define rep(x,a,b) for(int x=(a);x<=(b);x++)
#define per(x,a,b) for(int x=(a);x>=(b);x--)
#define reP(x,a,b) for(int x=(a);x<(b);x++)
#define Per(x,a,b) for(int x=(a);x>(b);x--)
#define scf(a) scanf("%d",&a)
#define scfll(a) scanf("%lld",&a)
#define scfdb(a) scanf("%lf",&a)
#define ptf(a) printf("%d",a)
#define ptfll(a) printf("%lld",a)
#define ptfsp(a) printf("%d ",a)
#define ptfllsp(a) printf("%lld ",a)
#define pli(a,b) make_pair(a,b)
#define pb push_back
#define el puts("")
#define FS first
#define SE second
#define PI acos(-1)
#define ls (pos<<1)
#define rs (pos<<1|1)
/*ios::sync_with_stdio(false);
freopen("in.txt","r",stdin);
freopen("1.out","w",stdout);*/
using namespace std;
const ll mod=1e9+7;
const int maxn=1e6+5;
int main(){
    ull x,y,a,b;
    scfll(x);scfll(y);scfll(a);scfll(b);
    ull res=0,ans=0;
    for(ll i=x;i<y;i=i*a){
        ans=max(ans,(y-i-1)/b+res);
        if((double)i*a>(double)y) break;
        res++;
    }
    cout<<ans;
}
