codeforces 165B（Burning Midnight Oil）

 1 #include<iostream>
 2 using namespace std;
 3 int ok(int v,int k)
 4 {
 5    int sum=v;
 6    while(v!=0)
 7    {
 8        sum+=v/k;
 9        v/=k;
10    }
11    return sum;
12 }
13 int main()
14 {
15     int n,k;
16     while(cin>>n>>k)
17     {
18        int up,low,ans=1;
19        if(n>k)
20        {
21         up=n;low=1;
22         while(low<=up) 
23         {
24            int mid=(up+low)/2;
25            int num=ok(mid,k);
26            if(num>=n) {up=mid-1;ans=mid;}
27            else low=mid+1;  
28         }   
29        }
30        else 
31        {
32          up=k;low=1;
33           while(low<=up) 
34         {
35            int mid=(up+low)/2;
36            int num=ok(mid,k);
37            if(num>=n) {up=mid-1;ans=mid;}
38            else low=mid+1;  
39         }    
40        }
41        
42         cout<<ans<<endl;
43     }
44     return 0;
45 }