2013nanjignB

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<algorithm>
 6 #include<vector>
 7 #define M(a,b) memset(a,b,sizeof(a))
 8 #include<map>
 9 #include<stdlib.h>
10 #define eps 1e-5
11 using namespace std;
12 
13 double x,y;
14 
15 int main()
16 {
17   while(scanf("%lf%lf",&x,&y)==2)
18   {
19       double lim = (y+1)/x-eps;
20       double pri = 1;
21       int num = 1;
22       int tim = 0;
23       double all = 1;
24       if(x>y) {puts("-1"); continue;}
25       while(1)
26       {
27           if(all-y>0||fabs(all-y)<eps)
28             break;
29           //cout<<lim<<endl;
30           int tmp = (int)((lim - pri)/(1.0/num));
31           pri+=tmp*(1.0/num);
32           //cout<<pri<<‘ ‘<<tmp<<endl;
33           tim+=tmp;
34           all+= tmp;
35           if(tmp==0)
36           {
37               int tm = (int)(1.0/(lim-pri)-num)+1;
38               if(tm>(y+1-eps-all)/pri)
39                 tm = (int)((y+1-eps-all)/pri);
40               num+=tm;
41               tim+=tm;
42               all+=pri*tm;
43           }
44          // cout<<tim<<endl;
45           //cout<<all<<endl;
46       }
47       printf("%d\n",tim);
48   }
49   return 0;
50 }