http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=883
#include<stdio.h>
#include<math.h>
int main()
{
    int k,n;
    while(scanf("%d%d",&k,&n)!=EOF)
    {
        int i,t;
        double f[11][101];
        for(i=0;i<=k;i++)
            f[i][1] = 1;
        for(t = 2; t<=n;t++)
        {
            for(i=0;i<=k;i++)
            {
                f[i][t] = f[i][t-1] ;
                if(i+1<=k)
                   f[i][t] += f[i+1][t-1];
                if(i-1>=0)
                   f[i][t] += f[i-1][t-1];
            }
        }
        double sum=0.0,p;
        for(i=0;i<=k;i++)
            sum += f[i][n];
        p = sum / pow((double)(k+1),(double)n);
        printf("%.5lf\n",p*100);
    }
    return 0;
}