cf B. Number Busters

http://codeforces.com/contest/382/problem/B

题意：给你Aa,b,w,x,c，然后每经过1秒，c=c-1;  如果b>=x,b=b-x;否则 a=a-1,b=w-(x-b);  问经过多少秒c<=a;

#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=0,r=200000000000000;
           if(c<=a)
           {
               printf("0
");
               continue;
           }
           b=w-b-1;
           while(l<r)
           {
             ll mid=(l+r)/2;
             ll aa=a-(b+mid*x)/w;
             ll cc=c-mid;
             if(cc<=aa) r=mid;
             else l=mid+1;
           }
           printf("%I64d
",l);
    }
}