1 #include<stdio.h>
 2 int main()
 3 {
 4     int n,i,t;
 5     float q,s;
 6     while(scanf("%d%f",&n,&q)==2)
 7     {
 8         if (n>=2&&n<=20&&q>0&&q<2)
 9         {
10             s=0;
11             for (i=0;i<=n;i++)
12             {
13                 s=s+pow(q,i);
14             }
15             printf("%.3f\n",s);
16         }
17     }
18     
19 }