#include <cstdio>

 #include <cstring>

 #include <algorithm>

 #define ll __int64

 using namespace std;

 ll a,b,w,x,c;

 int main()

 {

     while(scanf("%I64d%I64d%I64d%I64d%I64d",&a,&b,&w,&x,&c)!=EOF)

     {

            ll l=,r=;

            if(c<=a)

            {

                printf("0\n");

                continue;

            }

            b=w-b-;

            while(l<r)

            {

              ll mid=(l+r)/;

              ll aa=a-(b+mid*x)/w;

              ll cc=c-mid;

              if(cc<=aa) r=mid;

              else l=mid+;

            }

            printf("%I64d\n",l);

     }

 }