#include
using namespace std;
bool check(int s,int n,int m,int x,int y)
{
if((s*x)>((n-s)*y+m))
return false;
else
return true;
}
int maximum_student(int n,int m,int x,int y)
{
int start=0;
int end=n;
int mid,ans;
while(start<=end)
{
mid=(start+end)/2;
bool r=check(mid,n,m,x,y);
if®
{
ans=mid;
start=mid+1;
}
else
end=mid-1;
}
return ans;
}
int main()
{
int n,m,x,y;
cin>>n>>m>>x>>y;
int ans=maximum_student(n,m,x,y);
cout<<ans;
return 0;
}