#include<bits/stdc++.h>
#define ll long long
using namespace std;
int main()
{
    ll a,b,c,d,count=1,x,y=0;
    cin>>a>>b>>c>>d;
    if(c*d<=b)cout<<-1<<endl;
    else
    {
        if((a+b)<=(c*d))cout<<1<<endl;
        else
        {
            count=1;
            x=a;
           while(1)
           {
               if(x<=(y*d)) {cout<<count-1<<endl;break;}
               x+=b;
               y+=c;
               count++;
           }
        }
    }
    return 0;
}

#include<cstdio>
#include<algorithm>
using namespace std;
long long a,b,c,d,x,ans;
int main(){
	scanf("%lld%lld%lld%lld",&a,&b,&c,&d);
	x=c*d-b;
	if(x<=0)ans=-1;
	else{
		ans=a/x;
		if(a%x)++ans;
	}
	printf("%lld",ans);
	return 0;
}