附上“AC”的代码，测试2遍均通过
#include <stdlib.h>
#include <string.h>
#include<iostream>
#include<cmath>
using namespace std;
int min(int a,int b){return a<b?a:b;}
void multiply(int *a,int *b,int *c,int la,int lb,int &lc)
{
 int i,j,tmp;
 for (i=0;i<la;i++)
 {
  tmp=0;
  for (j=0;j<lb&&i+j<125;j++)
  {
   c[i+j]+=a[i]*b[j]+tmp;
   tmp=c[i+j]/10000;
   c[i+j]=c[i+j]%10000;
  }
  if (tmp>0&&i+lb<125)
  {
   c[i+lb]+=tmp;
  }
 }
 lc=min(125,la+lb+2);
 while (c[lc-1]==0&&lc>0) lc--;
}
int main()
{
 char s[10];
 int binary[100],ans[100],tmp[100],la,lb,lt;
 int n,dot,i,j,count,r;
 bool div;
 while (cin.getline(s,10))
 {
  memset(binary,0,sizeof(0));
  memset(ans,0,sizeof(0));
  la=0;lb=0;
  r=0;
  for (i=0;i<6;i++)
  {
   if (s[i]=='.') 
    dot=5-i;
   else
   {
    r*=10;
    r+=s[i]-'0';
   }
  }
  while (r%10==0&&dot>0)
  {
   r/=10;
   dot--;
  }
  n=atoi(s+7);
  dot*=n;
  if (r<10000)
  {
   binary[0]=r;
   lb=1;
  }
  else
  {
   binary[0]=r%10000;
   binary[1]=r/10000;
   lb=2;
  }
  ans[0]=1;
  la=1;
  while (n>0)
  {
   div=n%2;
   n/=2;
   if (div)
   {
    memset(tmp,0,sizeof(tmp));
    multiply(binary,ans,tmp,lb,la,lt);
    for (i=0;i<lt;i++) ans[i]=tmp[i];
    la=lt;
   }
   memset(tmp,0,sizeof(tmp));
   multiply(binary,binary,tmp,lb,lb,lt);
   for (i=0;i<lt;i++) binary[i]=tmp[i];
   lb=lt;
  }
  if (dot==0) 
  {
   cout<<ans[la-1];
   for (i=la-2;i>=0;i--)
   {
    j=1000;
    while (j>0)
    {
     cout<<ans[i]/j%10;
     j/=10;
    }
   }
  }
  else
  if ((la-1)*4>dot)
  {
   cout<<ans[la-1];
   count=0;
   for (i=la-2;i>=0;i--)
   {
    j=1000;
    while (j>0)
    {
     cout<<ans[i]/j%10;
     j/=10;
     count++;
     if (count+dot==(la-1)*4) cout<<'.';
    }
   }
  }
  else
  if ((la-1)*4<=dot&&la*4>dot)
  {
   dot-=(la-1)*4;
   j=1000;
   count=0;
   while (j>0)
   {
    if (ans[la-1]/j>0) cout<<ans[la-1]/j%10;
    j/=10;
    count++;
    if (count+dot==4) cout<<'.';
   }
   for (i=la-2;i>=0;i--)
   {
    j=1000;
    while (j>0)
    {
     cout<<ans[i]/j%10;
     j/=10;
    }
   }
  }
  else
  if (dot>=la*4)
  {
   cout<<'.';
   for (i=0;i<dot-4*la;i++)
    cout<<0;
   for (i=la-1;i>=0;i--)
   {
    j=1000;
    while (j>0)
    {
     cout<<ans[i]/j%10;
     j/=10;
    }
   }
  }
  cout<<endl;
 }
 return 0;
}