include<bits/stdc++.h>

define ll long long

using namespace std;
ll a,b,c,d;
int main()
{
cin>>a>>b>>c>>d;
if(a==0)
{
cout<<0;
return 0;
}
if(cd<=b)
{
cout<<-1;
return 0;
}
cout<<(a/(cd-b)+1);
}