codeforces 224 B. Number Busters

#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
#define LL long long
LL a,b,w,x,c;
bool judge(LL t)
{
	if(b-x*t>=0)
		return c-t<=a;
	return c-t<=a-((x*t-b)/w+((x*t-b)%w!=0));
}
int main()
{
	while(cin>>a>>b>>w>>x>>c)
	{
		if(c<=a)
		{
			cout<<0<<endl;
			break;
		}
		LL l=1;
		LL r=(LL)1<<60;
		while(l+3<r)
		{
			LL mid=(l+r)>>1;
			if(judge(mid))
				r=mid;
			else
				l=mid;
		}
		for(LL i=l;i<=r;i++)
			if(judge(i))
			{
				cout<<i<<endl;
				break;
			}
	}
	return 0;
}