cf B. Vasily the Bear and Fly

http://codeforces.com/contest/336/problem/B

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <cmath>
 using namespace std;

 int main()
 {
     int m,r;
     scanf("%d%d",&m,&r);
     double sum=;
     for(int i=; i<m; i++)
     {
         if(i==) sum+=*r*m;
         else if(i==) sum+=(*r+sqrt()*r)*(*m-);
         else
         {
             sum+=(*m-*i)*(((*i-)+sqrt())*r);
         }
     }
     printf("%lf\n",sum/m/m);
     return ;
 }