long long a[48]={1,1,2,3,5,8,13,21,34,55,
89,144,233,377,610,987,1597,2584,4181,6765,
10946,17711,28657,46368,75025,121393,196418,317811,514229,832040,
1346269,2178309,3524578,5702887,9227465,14930352,24157817,39088169,63245986,102334155,
165580141,267914296,433494437,701408733,1134903170,1836311903,2971215073,4807526976};
cout<<a[n-1]<<".00";
这样没啥问题。