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=,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);
     }
 }