#include<bits/stdc++.h>
using namespace std;
bool check(int n,int m,int x,int y,int mid){
int val1 = mid*x;
int val2 = m + (n-mid)*y;
if(val1<=val2){
return true;
}
return false;
}
int ans(int n,int m,int x,int y){
int start = 0;
int end = n;
int ans = -1;
while(start<=end){
int mid = (start+end)/2;
bool check1 = check(n,m,x,y,mid);
if(check1==true){
ans = mid;
start = mid + 1;
}else{
end = mid - 1;
}
}
return ans;
}
int main() {
int n;
cin>>n;
int m;
cin>>m;
int x;
cin>>x;
int y;
cin>>y;
cout << ans(n,m,x,y) << endl;
}