参考博客：

http://blog.zhengyi.one/fibonacci-in-logn.html

原文是用python实现，这里改写成C++

 

#include <cstdio>
#include <cstring>
#include <algorithm>
 
using namespace std;
const int mod = 1000000007;
typedef long long LL;
 
struct matrix{
    LL m[2][2];
};
const matrix E = {  
    1, 1,
    1, 0,
};
 
matrix multi(const matrix &a, const matrix &b)  // 矩阵乘法
{
    matrix c;
    for(int i=0; i<2; i++)
    {
        for(int j=0; j<2; j++)
        {
            c.m[i][j] = 0;
            for(int k=0; k<2; k++)
                c.m[i][j] = (c.m[i][j] + a.m[i][k] * b.m[k][j]) % mod;
        }
    }
    return c;
}
 
matrix pow_mod(LL n)    // 快速幂运算
{
    matrix res = E, a = E;
    while(n)
    {
        if(n&1)
            res = multi(res, a);
        a = multi(a, a);
        n = n/2;
    }
    return res;
}
 
 
int main()
{
    LL n;
    scanf("%lld", &n);
    printf("%lld\n", pow_mod(n).m[0][1]);
    
 
 
    return 0;
}