//~ author      : Sumit Prajapati
#include <bits/stdc++.h>
using namespace std;


#define ull                 unsigned long long
#define ll                  long long
#define int                 long long           
#define pii                 pair<int, int>
#define pll                 pair<ll, ll>
#define pb                  push_back
#define mk                  make_pair
#define ff                  first
#define ss                  second
#define all(a)              a.begin(),a.end()
#define trav(x,v)           for(auto &x:v)
#define rep(i,n)            for(int i=0;i<n;i++)
#define repe(i,n)           for(int i=1;i<=n;i++)
#define read(a,n)           rep(i,n)cin>>a[i]
#define reade(a,n)          repe(i,n)cin>>a[i]
#define FOR(i,a,b)          for(int i=a;i<=b;i++)
#define printar(a,s,e)      FOR(i,s,e)cout<<a[i]<<" ";cout<<'\n'
#define curtime             chrono::high_resolution_clock::now()
#define timedif(start,end)  chrono::duration_cast<chrono::nanoseconds>(end - start).count()




auto time0 = curtime;
const int MD=1e9+7;
const int MDL=998244353;
const int INF=1e9;
const int MX=1e5+5;

 
 
 
 
void solve(){
  
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    rep(k,MX){
        int cyan=a+k*b;
        int red=d*k*c;
        if(cyan<=red){
            cout<<k<<"\n";
            return;
        }

    }
    cout<<"-1\n";

} 
 
 
int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    time0 = curtime;
    srand(time(NULL));
    int t=1;
    // cin>>t;
    repe(tt,t){
        // cout<<"Case #"<<tt<<": ";
        solve();
    }
    
    // cerr<<"Execution Time: "<<timedif(time0,curtime)*1e-9<<" sec\n";
    return 0;
 
}

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#ifdef ENABLE_DEBUG
#define dump(a) cerr<<#a<<"="<<a<<endl
#define dumparr(a,n) cerr<<#a<<"["<<n<<"]="<<a[n]<<endl
#else
#define dump(a) 
#define dumparr(a,n) 
#endif
#define FOR(i, a, b) for(ll i = (ll)a;i < (ll)b;i++)
#define For(i, a) FOR(i, 0, a)
#define REV(i, a, b) for(ll i = (ll)b-1LL;i >= (ll)a;i--)
#define Rev(i, a) REV(i, 0, a)
#define REP(a) For(i, a)
#define SIGN(a) (a==0?0:(a>0?1:-1))

typedef long long int ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef pair<ll, ll> pll;
typedef pair<ll,pll> ppll;
typedef vector<ll> vll;
typedef long double ld;
typedef pair<ld,ld> pdd;

pll operator+(pll a,pll b){
  return pll(a.first+b.first,a.second+b.second);
}
pll operator-(pll a,pll b){
  return pll(a.first-b.first,a.second-b.second);
}
pll operator*(ll a,pll b){
  return pll(b.first*a,b.second*a);
}
const ll INF=(1LL<<60);
#if __cplusplus<201700L
ll gcd(ll a, ll b) {
  a=abs(a);
  b=abs(b);
  if(a==0)return b;
  if(b==0)return a;
  if(a < b) return gcd(b, a);
  ll r;
  while ((r=a%b)) {
    a = b;
    b = r;
  }
  return b;
}
#endif
template<class T>
bool chmax(T& a,const T& b){
  if(a<b){
    a=b;
    return true;
  }
  return false;
}
template<class T>
bool chmin(T& a,const T& b){
  if(a>b){
    a=b;
    return true;
  }
  return false;
}
template<class S,class T>
std::ostream& operator<<(std::ostream& os,pair<S,T> a){
  os << "(" << a.first << "," << a.second << ")";
  return os;
}
template<class T>
std::ostream& operator<<(std::ostream& os,vector<T> a){
  os << "[ ";
  REP(a.size()){
    os<< a[i] << " ";
  }
  os<< " ]";
  return os;
}


ll solve(long long X, long long Y){
  static map<ll,ll> cache;
  if(cache.count(Y)){
    return cache[Y];
  }
  if(X>=Y){
    return X-Y;
  }
  ll ret=abs(X-Y);
  if(Y%2){
    chmin(ret,solve(X,(Y+1)/2)+2);
    chmin(ret,solve(X,(Y-1)/2)+2);
  }else{
    chmin(ret,solve(X,Y/2)+1);
  }
  return cache[Y]=ret;
}

int main(){
  cout<<setprecision(1000);
    long long X;
    scanf("%lld",&X);
    long long Y;
    scanf("%lld",&Y);
    cout<<solve(X, Y)<<endl;;
    return 0;
}
