玄关

#include <iostream>
#include <cmath>

using namespace std;

#define int long long
const int mod = 1e9 + 7;

int n;

int F(int num)
{
	long double a = 1 + sqrt(5),b = 1 - sqrt(5);
	long double x = pow(a,num),y = pow(b,num);
	long double z = sqrt(5);
	long double c = pow(2,num);
	return (x - y) / (z * c);
}

signed main() 
{
	cin >> n;
	cout << F(n) % mod;
	return 0;
}

做法： 结果：$\textcolor{red}{Wrong Anser}$ #6~#11