#include<bits/stdc++.h>
#define ll long long
using namespace std;
int main()
{
    ll a,b,c,d;
    cin>>a>>b>>c>>d;
    ll count=0;
    ll cyan=a;
    ll red=0;
    
    while(cyan>red)
    {
        if(count>100000)
        {
            cout<<-1<<endl;
            return 0;
        }
        cyan+=b;
        red+=c;
        count++;
        if(cyan<=red*d)
        break;
    }
    cout<<count<<endl;
    
}
#include <iostream>
#include <vector>
#include <unordered_map>
#include <deque>
#include <list>
#include <set>
#include <random>
#include <deque>
#include <unordered_set>



using namespace std;
using ll = long long;
const ll BIG = 1000000007;

int main() {
    ll x1,y1,x2,y2;
    cin >> x1 >> y1 >> x2 >> y2;
    if(x1 == x2 && y1 == y2){
        cout << 0 << endl;
    }
    else if((x1 + y1) == (x2 + y2) || (x1 - y1) == (x2 - y2) || (abs(x1 - x2) + abs(y1 - y2)) <= 3){
        cout << 1 << endl;
    }
    else{
        if((x1 + y1) % 2 == (x2 + y2) % 2){
            cout << 2 << endl;
        }
        else{
            for(ll x = x1 - 3;x <= x1 + 3;++x){
                for(ll y = y1 - 3;y <= y1 + 3;++y){
                    if((abs(x - x1) + abs(y - y1)) <= 3){
                        if(((x + y) == (x2 + y2)) || ((x - y) == (x2 - y2))){
                            cout << 2 << endl;
                            return 0;
                        }
                    }
                }
            }
            cout << 3 << endl;
        }
    }
}



